Many different “rashes” present with red patches and plaques. When these disorders occur on dry, keratinized skin, they usually exhibit distinct differentiating features that indicate a specific diagnosis. However, when these conditions occur on warm, moist skin such as the anogenital region, they more often display nonspecific erythema with no, or only barely visible, scale (Fig. 5-1
). Therefore, making a diagnosis on the basis of examination alone may not be possible. Other approaches, such as whole-body examination, eliciting a history of itching, listing of locally applied contactants, obtaining microbial cultures, and performing biopsies, may be necessary. In spite of all this, at times, a definitive diagnosis just cannot be made. When this occurs, and when culture and biopsy have ruled out infections and malignancy, symptomatic therapy is permissible. Such therapy usually includes the use of topical steroids to reduce itching and the redness related to underlying inflammation. Please note that, in the absence of significant infection, such topical steroid treatment will rarely, if ever, be detrimental to the underlying disorder.
SECTION A: DERMATITIS AND LICHENIFICATION
Anogenital pruritus occurs in two settings. It may arise from visibly normal-appearing tissue (“primary” pruritus) or it may occur as part of an already visible disorder (“secondary” pruritus). The red patches and plaques that have an “eczematous” appearance are discussed here in Section A. These include both examples of primary pruritus (atopic dermatitis and lichen simplex chronicus [LSC]) and examples of secondary pruritus (contact dermatitis and seborrheic dermatitis). Primary pruritus that uncommonly presents with an eczematous appearance such as idiopathic (“essential”) pruritus is discussed in Chapter 13
. And, those instances of secondary pruritus that less frequently demonstrate an eczematous appearance secondary to the itching (eg, psoriasis, lichen sclerosus, and tinea cruris) are dealt with as these individual disorders are covered throughout the book.
Conceptually, it is worth trying to separate primary from secondary pruritus, but since some scratching often occurs in both settings, the clinical appearance at the time of examination may not allow one to separate the two processes. When that is the case, treatment specifically directed toward the cessation of scratching may allow for correct identification. That is, if the scratching can be stopped, the scratched tissue will either return to normal (primary pruritus) or will likely reveal the nature of the underlying disorder (secondary pruritus).
Obviously it is important, then, to understand what constitutes an “eczematous” appearance.
The following is a short review of terminology for dermatitic/eczematous disorders previously covered in Chapter 2
. The two adjectives “eczematous” and “dermatitic” (which like the nouns “eczema” and “dermatitis”) are synonyms, and they can be defined morphologically. The morphologic appearance of the eczematous disease is classically defined by the presence of solid plaques or plaques made up of closely set red papules. These plaques are characterized by (1) poorly marginated borders, (2) overlying scale, and (3) the presence of epithelial disruption and/or lichenification. Epithelial disruption
is most often noted by the presence of excoriations, but other signs of epithelial disruption may also be present. These include weeping, crusting, fissuring, or the presence of yellow-colored scale. This yellow color is owing to the presence of small amounts of plasma that coats the otherwise gray, white, or silver color of scale. When rubbing is more prominent than scratching, the calluslike response of lichenification may supplant much of the evidence for epithelial disruption. Lichenification
is recognized clinically by three features: (1) palpably thickened skin, (2) exaggerated skin markings, and (3) lichen-type scale. Lichen-type scale, because of its tight adherence to the underlying epithelium, is more or less colorless when dry but whitens when it absorbs moisture. This whitening often happens in the anogenital area because of retained sweat.
Fig. 5-1. Red, scaling diseases in damp skin folds often do not show obvious scale; this woman has psoriasis that appears shiny rather than showing the classic heavy white scale of psoriasis in other locations.
Lesions possessing an eczematous clinical appearance have a characteristic histological appearance as well. This microscopic appearance on biopsy demonstrates spongiotic inflammation
(inflammatory cells accompanied by intercellular and intracellular edema within the epithelium) when the process is acute and by acanthosis
(epithelial thickening often termed “psoriasiform dermatitis”) when the process is chronic and lichenified. This is the microscopic appearance common to all of the disorders discussed in Section A of this chapter. Since all of these eczematous disorders share this common histologic appearance, pathologists are usually unable to separately identify each of the conditions that exist within the general category of eczematous disease. For this reason, when the pathologist reports either “spongiotic dermatitis” or “psoriasiform dermatitis,” it is usually necessary for the clinician to make a clinical-pathologic correlation in order to arrive at a more specific diagnosis.1
Atopic Dermatitis and Lichen Simplex Chronicus
Atopic dermatitis and LSC are examples of primary pruritus in which itching occurs in clinically normal-appearing tissue. This itching leads to vigorous scratching and/or rubbing. The nomenclature regarding atopic dermatitis and its variants is somewhat complex and controversial. The term “atopy” has been defined in many ways, but most often, the definition includes a genetic predisposition for the development of hypersensitivity wherein IgE-mediated reactions occur as a result of exposure to common environmental antigens. Thus, atopic individuals frequently develop allergic rhinitis (hay fever), asthma, and/or atopic dermatitis. A semantic problem arises when an eczematous eruption occurs in an individual who lacks a personal or prominent family history of hay fever or asthma. In this setting, the eczematous process has variously been termed neurodermatitis, infantile eczema, childhood eczema, or LSC. Given the lack of consensus regarding the diagnostic criteria for atopic dermatitis and in view of the fact that these eczematous eruptions share the presence of the “itch-scratch cycle” (see below and Chapter 2
), I believe it is best, or at least less confusing, to use the term atopic dermatitis (for the multifocal
form of the disorder) and LSC (for the localized
form of the disorder) of the condition regardless of whether or not the individual has other clinical evidence of atopy. Moreover, since anogenital eczematous involvement very often occurs in the absence of eczematous disease elsewhere, we will generally refer to it as LSC.
Atopic dermatitis in its multifocal form is a very common disorder with a point prevalence of about 4%-5% of adults in Western countries.2
The localized form of atopic dermatitis, anogenital LSC, occurs in both sexes and at all ages. It is commonly encountered in those who are adults, and in this group, there is evidence that it occurs in women a little more frequently than in men.3
It occurs a little less frequently in children, but when it does, we believe that boys are affected somewhat more often than do girls. The prevalence and incidence of localized anogenital LSC are not known with certainty, but in one of the larger studies, such patients accounted for 1.5% of all visits to a dermatology clinic.4
Based on a few older studies, discussion at conferences, and our own experience, it is probably the single most common symptomatic condition involving the anogenital area.
As indicated above, LSC shares the morphological characteristics of all eczematous diseases. This includes erythematous, poorly marginated, scaling papules and plaques with evidence of epithelial disruption and/or lichenification (Figs. 5-2
). But in contrast to other eczematous diseases, the severity of excoriation and/or lichenification often allows for correct clinical identification. This may not be true in mild cases where the warm, moist environment of the anogenital area might obscure some of the characteristic morphological features. Thus, scale may not be as visibly apparent (though it can still be recognized by at least some roughness on palpation) as it is with LSC in other dryer regions of the body (Figs. 5-8
). This scale is hydrophilic, and when it takes up water, it whitens. The white color can be fairly prominent when a patient first undresses but decreases with time as evaporation reduces the moisture content of the surface epithelium (Figs. 5-10
). Moreover, deep scratching may destroy or remove melanocytes, leaving hypopigmented areas when the scratch marks heal (Fig. 5-13
). Alternatively, if rubbing supplants scratching, the involved area may become hyperpigmented due to chronic inflammatory stimulation of melanocytes. Such hyperpigmentation can decrease the apparentness of erythema, leading one to underestimate the amount of inflammation that is present (Figs. 5-14
). Hyperpigmentation is especially likely to develop in patients with naturally dark skin.
Fig. 5-2. Classic lichen simplex chronicus exhibits poorly demarcated erythematous lichenification, seen here on the hair-bearing surface of the labia majora. There is an irregular erosion from scratching as well.
Fig. 5-3. This woman has remarkably thickened skin from rubbing and scratching, with classic deepened skin markings. Rather than erythema, this patient of color shows surface white color from hydrated epithelium.
Genital LSC in women primarily occurs on the outer aspects of the labia majora though involvement of the labia minora is sometimes seen. In men, the scrotum is the predominant site of involvement, but the base, or even the entire shaft, of the penis are sometimes affected (Fig. 5-16
). In both sexes, there may be involvement of the anal and/or perianal area (Fig. 5-17
Fig. 5-4. Scale is abundant, as is redness on the scrotum of this man with severe pruritus who had recently been admitted to the hospital with an incorrect diagnosis of cellulitis.
Fig. 5-5. The prominent lichenification produces thicker skin without the usual softer folds of the labia majora.
Fig. 5-6. Poorly demarcated red plaques with lichenification are classic for LSC; her lichenification is more prominent on the left labium majus than the right.
Fig. 5-7. Lichen simplex chronicus of the male genitalia is usually on the scrotum and again exhibits poorly demarcated erythema, lichenification, and superficial erosions produced by chronic rubbing and scratching.
Fig. 5-8. Although the thickened labia majora in this patient do not appear to have scale because of the damp environment, the surface is rough to the touch, signifying the presence of scale.
Fig. 5-9. The surface of the scrotum again is very rough in this patient with lichen simplex chronicus, in contrast to the apparent nonscaling appearance.
Fig. 5-10. This patient with unilateral lichenification of LSC also shows white surface discoloration from the damp environment.
Fig. 5-11. Fairly often, LSC is unilateral, as seen here in this woman with LSC on the medial right labium majus, white from the environment.
Fig. 5-12. The inflammation and damage of rubbing can precipitate vitiligo, where this disease of depigmentation occurs preferentially in areas of trauma or irritation; this is more easily seen in patients who are darkly pigmented and can be mistaken for lichen sclerosus. The hyperpigmented, thickened skin represents LSC.
Fig. 5-13. This vulva shows white linear lesions where melanocytes were removed by forceful scratching.
Fig. 5-14. Inflammation in dark-complexioned people appears hyperpigmented rather than red. Sometimes, lichenification and the compact, lichenoid scale appear shiny, as though the skin has been polished from the frequent rubbing.
Fig. 5-15. This scrotum shows dark brown lichenification, due both erythema seen through dark skin and coexisting postinflammatory hyperpigmentation.
Fig. 5-16. Although male LSC is usually scrotal, sometimes the penis is involved as well; in addition to classic scrotal LSC, the penile shaft is both lichenified and thickened from underlying fibrosis from years of rubbing and scratching.
LSC is a chronic disease. Left untreated, the itchscratch cycle persists indefinitely, although it can be episodic rather than consistently present. This process is extremely discomforting for the patient, and it may lead
to a significant decrement in quality of life.10
Other troublesome sequelae may include hyperpigmentation and hypopigmentation due to either activation or destruction of melanocytes, respectively. Treatment for LSC can be extremely effective (Figs. 5-20
). Approach to therapy includes five basic steps: (1) improvement in the local environment to reduce the triggering that leads to itching and scratching, (2) restoration of normal barrier layer function, (3) reduction in inflammation, (4) cessation of the itch-scratch cycle, and (5) identification and treatment for any detrimental psychological factors that may be present.
Fig. 5-20. Lichenified lichen simplex chronicus before treatment.
Fig. 5-21. Five weeks later, the LSC has cleared and the vulva appears normal.
Improvement in the Local Environment
As mentioned previously, heat and sweat act as provoking factors for the development of itching, scratching, and inflammation. Removing or reducing these factors is certainly desirable but is more difficult to do than one might expect. Immediate steps include a change to less occlusive, less tight-fitting clothing and the use of materials (such as cotton and cotton-blends) that allow for better movement of air. Other approaches we recommend include the avoidance of prolonged sitting, the use of cloth rather than vinyl for seating surfaces, and the use of cooler temperatures in the workspace or home. Weight loss can help those who are obese by way of decreasing intertriginous surface area and reducing frictional rubbing through body movement. Note that the use of a hair dryer even on its lowest temperature settings in an attempt to dry the area is not helpful, and in most instances, it is detrimental.
Other irritants such as fecal contamination, urinary incontinence, and vaginal secretions should be dealt with. Treatment of fecal and urinary incontinence lies outside the scope of this chapter; additional medical consultation will probably be necessary for amelioration of these two factors. Vaginal discharge needs to be properly diagnosed and treated (see Chapter 14
), and the continual use of panty liners should be discouraged. Asking patients about the frequency and nature of their anogenital hygiene is important because many patients, particularly women, think of the anogenital area as a site “that is especially dirty.” Excessive hygiene especially using water that is too hot, harsh cleaning products, and excessive scrubbing removes natural skin lubricants and thus can cause irritation. Contrary to decades of physician recommendations, such as using only white underwear, the avoidance of dyes in clothing lacks documented scientific merit. Again, contrary to popular opinion, laundering practices
for underwear (number of rinses, avoidance of certain detergents, discontinuation of antistatic dryer strips, etc.) are for practical purposes never an important triggering factor.
Restoration of Barrier Layer Function
Barrier layer dysfunction occurs in all patients with atopic dermatitis/LSC. This dysfunction can occur as a result of genetic factors that interfere with epithelial cell differentiation, irritant factors mentioned above, and physical disruption of the surface epithelium due to scratching and rubbing. The approach to all three of these factors involves the use of lubrication. Since lubricants are covered in detail in Chapter 3
, this material will not be repeated here. Irritants are dealt with in the preceding two paragraphs. Reduction of itching, scratching, and rubbing is covered in the several paragraphs that follow.
Reduction in Inflammation
Steroids, used topically or systemically, are the sine qua non
for the treatment of inflammation. This subject is covered thoroughly in the section titled “Anti-inflammatory Therapy” of Chapter 3
and, other than mention of a few important principles, will not be repeated here. First, the strength of the topical steroid must be appropriate both for patient safety and the task at hand. Lowand mid-potency steroids such as hydrocortisone and triamcinolone are usually ineffective in anogenital LSC/atopic dermatitis. Second, an ointment vehicle, rather than a cream, will be better tolerated and adds a bit of lubrication. Third, topical steroids must be continued for a month or more after the clinical symptoms and signs have regressed. However, after clinical clearing, the frequency of application and/or the potency of the topical steroid should be tapered. A lengthy duration of therapy is necessary because microscopic evidence of inflammation remains for a considerable period of time after clinical improvement, or even resolution, is noted. Fourth, if topical steroids have not been effective after a month of treatment, consider the use of systemic steroid therapy. While a “burst” of prednisone can work, it is usually too short to be maximally effective, and in addition, rebound often occurs shortly after the last pills are administered. For this, and other, reasons, we prefer the use of intramuscularly administered triamcinolone acetonide (Kenalog) as described in Chapter 3
Occasionally, a patient requires additional anti-inflammatory medication. There are several topical options. The use of nonsteroidal topical calcineurin inhibitors tacrolimus and pimecrolimus (see Chapter 3
) in an attempt to reduce the side effects of prolonged steroid use may be considered, but the stinging on application and efficacy less than mid- and high-potency topical steroids represent significant limitations.13
Crisaborole ointment has also been available for several years, approved in the United States as a nonsteroidal medication for atopic dermatitis. This medication has not found a useful place in the practical treatment of inflammatory dermatoses. At the time of this writing, the Food and Drug Administration has accepted ruxolitinib cream, a janus kinase inhibitor, for priority review for atopic dermatitis.
Until recently, the only systemic anti-inflammatory agents used routinely for eczematous diseases were corticosteroids. Cyclosporine is very effective but dangerous for long-term use. However, the development of biologic medications for inflammatory diseases has exploded in the last 20 years. Dupilumab (Dupixent) is the only currently available biologic medication used for eczematous diseases, and this medication has shown remarkable benefit with a good safety profile for patients with recalcitrant disease.14,15
This medication blocks IL-4 and IL-13 signaling. There are a number of additional biologic agents in development for eczema, including lebrikizumab, tralokinumab, nemolizumab, tezepelumab, and ISB 830.16
Breaking the Itch-Scratch Cycle
This is probably the single most important aspect in the treatment of LSC. Unfortunately, it is also the most often overlooked. Fortunately, the presence of clothing, a conscious attempt to control scratching, and embarrassment associated with genital scratching tend to reduce much of daytime scratching. However, these constraints are lessened when the patient is at home in the evening and are removed completely while sleeping. Thus, the nighttime scratching that characteristically is present with the itch-scratch cycle remains in place. Approaches for the treatment of nighttime rubbing and scratching are thoroughly covered in Chapter 3
, but several major principles are worth reviewing here. First, nighttime scratching occurs periodically while the patient is in the lighter stages of non-REM sleep.5,6
Nonhabituating medications with a sedative effect such as the first generation of antihistamines and certain tricyclics work well for this purpose. Second, the dose of the medication chosen should be increased weekly until nighttime scratching ceases or until the risks of side effects caution against any further increase. Third, the medication should be taken about 2 hours before going to bed to both prevent scratching before actually falling asleep and to reduce possible morning “hangover.” Fourth, the medication should be taken every evening rather than on an “as necessary” basis.
In many instances, sedating therapy for nighttime scratching obviates the need to treat daytime itching with medications, such as hydroxyzine, that can cause sleepiness, inept driving, or dangerous operation of machinery. However, some patients will still experience significant daytime pruritus. Many clinicians prescribe nonsedating antihistamines for these individuals. Unfortunately, this approach does not work well probably because histamine
plays only a minor role in the itching associated with atopic dermatitis and LSC. In this situation, I prefer the use of selective serotonin reuptake inhibitors (SSRIs). It is not clear whether these agents work because of their beneficial effect on anxiety and depression or whether they diminish the obsessive-compulsive component of chronic scratching. There is limited support for this approach in the medical literature.17,18
Further information on the use of SSRIs can be found in Chapter 3
Identification and Treatment of Detrimental Psychological Components
Anxiety and/or depression are regularly present in patients with LSC.12,19
Most patients will not volunteer this information unless it is directly sought by a clinician. Even then, the importance of psychological factors tends to be minimized by patients, and thus, clinician questioning in this area should occur not just initially but also periodically at the time of return visits. Some controversy exists as to whether these psychological factors play a role in the etiology of the LSC/atopic dermatitis or whether they are secondary to the presence of these disorders. It is my opinion, supported by some published data, that they frequently play a role in causation. But, either way, once identified, treatment, generally with SSRIs as described in Chapter 3
, can be quite helpful.
In addition to the common problems of anxiety and depression, patients with LSC/atopic dermatitis may also experience sexual dysfunction.20,21
Although most of us would not consider ourselves as expert in the area of sexual counseling, giving patients an opportunity to discuss this aspect of their lives, either with us or with a trained therapist, can be quite beneficial in the treatment of patients with anogenital LSC.
Irritant Contact Dermatitis
Irritant contact dermatitis is an eczematous reaction that develops in response to an exogenous substance that can cause inflammation when applied to the skin of any individual. Thus, all individuals have the potential for developing irritant contact dermatitis, whereas only patients specifically sensitized to an allergen develop allergic contact dermatitis (ACD).
The prevalence of irritant contact dermatitis involving the anogenital area is unknown. However, a major study indicated that irritant contact dermatitis accounted for about 15% of all patients with anogenital problems referred to dermatologists for patch testing (see the supplementary online content for Ref.3
). Irritant contact dermatitis is often divided into two categories: chronic and acute irritant contact dermatitis.
Fig. 5-22. This erythematous plaque is typical of chronic irritant dermatitis, here produced by washing with soap and water multiple times each day.
irritant contact dermatitis is usually manifested by symptoms of irritation, burning, pain, soreness, or rawness. Note that in some patients, especially those who are genetically atopic, the irritant can also cause itching and can initiate an itch-scratch cycle. Generally, chronic irritant contact dermatitis presents as a poorly demarcated, slightly scaly erythematous patch or slightly elevated plaque. Little or no edema is present (Fig. 5-22
). The red hues sometimes occur at the dusky red or brownred end of the erythema spectrum (Fig. 5-23
). Often, there
is a dry, glazed, fissured, chapped appearance (Figs. 5-24
). If the irritant in question triggers itching and scratching, the morphology will be indistinguishable from that of LSC.
Fig. 5-23. The red-brown color of this poorly demarcated plaque of irritant contact dermatitis is characteristic and produced here by chronic incontinence.
Fig. 5-24. At times, irritant dermatitis can appear red and glazed, as seen here in this patient who was using witch hazel on the vulva to stop itching.
Acute irritant contact dermatitis is essentially a chemical “burn.” It is characterized as a rapid development of erythema, edema, and sometimes blistering shortly after the contact occurs (Fig. 5-26
). Poorly keratinized skin, such as the modified mucous membranes of the vulva, the glans penis, and the inner aspect of the prepuce, is very fragile, and blister roofs are shed quickly, forming erosions or even ulcers (Fig. 5-27
). On the more resilient keratinized skin, blisters may remain visible for a day or two before they also become unroofed, leaving erosions or ulcers (Fig. 5-28
Fig. 5-25. The shiny, chapped appearance of this irritant contact dermatitis was produced by diarrhea.
Fig. 5-26. Caustic substances, including chronic exposure to urine and feces can produce erosions and ulcerations.
The most important aspects of therapy are the identification and elimination of all irritants. Irritant contact dermatitis in the genital area is often multifactorial, so that anything applied to the anogenital area to include all medications, soaps, antiseptics, douches, and powders should be discontinued. Vigorous cleansing should also be stopped. Note, however, that some patients become “addicted” to certain behaviors, and as a result, there may be very poor compliance with instructions to cease these ritualistic behaviors. After the offending agent or agents are discontinued and use of a mid-potency topical corticosteroid ointment has been instituted, the dermatitis quickly improves. If the skin is dry and chapped, lubricants (see Chapter 3
) may be useful. Infants and diapered adults may require the use of a simple “barrier” product such as zinc oxide ointment to keep urine and feces away from the skin. In those instances where itching or pain is really troublesome, prednisone, at a dose of 40 mg each morning for a few days, can improve this symptom until healing is well underway, at which point a topical corticosteroid can be substituted.
The pain and burning of acute irritant contact dermatitis can be minimized through the use of tepid tap water bathtub soaks several times a day for the first few days. Lubrication with a thin layer of petrolatum should be applied immediately following each soak. Nighttime sedation and oral analgesics may be necessary for several days. Topical analgesics should be avoided as they may cause additional discomfort and may even worsen the problem through the development of an allergic reaction.
Allergic Contact Dermatitis
As opposed to irritant contact dermatitis wherein all individuals are potentially capable of developing a reaction, ACD requires immunological processing. This is a more restrictive process and only a limited number of individuals exposed to a potential allergen will develop ACD at the time of their subsequent contact with the offending agent.
Controversy exists regarding the frequency with which ACD of the anogenital region occurs. In the past, nearly all of the published material on prevalence dealt with clinically diagnosed vulvar involvement in women. However, more recently, the publications regarding ACD come from patch test clinics. These reports contain much more information on the perianal area and the genitalia in both men and women.3,22,23,24
These studies suggest that one or more clinically relevant positive patch test will be found in 40%-50% of all patients sent for patch testing.
There is, however, a problem with the data from patch test clinics. This difficulty revolves around determining which positive patch tests are actually clinically relevant. Most clinicians just assume that if the patient has applied something containing the allergen, it is relevant. This is not always true! Second, patients with “dermatitis” of all types frequently have several positive patch tests to common allergens. It is not known what role, if any, one or more of these allergens play in the pathogenesis of their dermatitis. This is particularly true for patients who actually have atopic dermatitis rather than ACD.25
Allergic contact dermatitis is clinically characterized by the presence of poorly marginated, bright red, edematous patches and plaques. Scale is generally less prominent than it is in both atopic dermatitis/LSC and irritant contact dermatitis. Pruritus is regularly present and, in some instances, can be quite problematic. Not surprisingly, this frequently results in superimposed development of the itch-scratch cycle and the clinical signs of LSC. Sometimes vesicles, usually minute in size (representing macroscopic evidence of histologic spongiosis), stud the surface of the erythematous plaques (Fig. 5-31
). Occasionally, odd shapes (linear or angular) are found (Fig. 5-32
). These generally occur by way of irregular application of medications applied with the finger tips. The labia majora are usually involved in women and both the penis and the scrotum may be affected in men (Figs. 5-34
). Anal and perianal involvement is commonly found in both sexes.24
Allergic contact urticaria
is a rarely encountered, separate, and distinct disorder from ACD. The appearance can be either that of tissue swelling (angioedema) or can develop as urticarial papules (wheals, hives) and plaques that are entirely similar to those that occur with
garden-variety urticaria. Unlike the situation with allergic contact dermatitis
, there is no clinical evidence of epithelial abnormalities. Such reactions are usually easy to recognize because of the rapid development of the urticarial reaction within minutes after contact has taken place. This allergic contact urticaria is particularly likely to occur in those who have become sensitized to latex or seminal fluid.
Fig. 5-31. These small, coalescing, firm vesicles are classic for allergic contact dermatitis.
Fig. 5-32. Linear plaques of fine vesicles are pathognomonic for allergic contact dermatitis to plants such as poison ivy.
Fig. 5-33. The unusual distribution of this red, scaling plaque on the buttocks and posterior thighs is consistent with the cause of this man’s allergic contact dermatitis; a teak toilet seat.
Fig. 5-34. These red, exudative lesions were produced by the application of triple antibiotic ointment, which contains the very strong antigen, neomycin.