Chronic constipation is often functional. The pediatrician can usually identify functional constipation by a thorough history and physical examination. Onset frequency usually occurs during one of the three periods: in infants transitioning to formula or solids, in toddlers acquiring toilet skills, or at the beginning of school. Children are described as standing on their toes, stiffening their legs, or hiding in a corner. The pain a child experiences is from the normal propagating contractions pushing against a closed external anal sphincter. Fecal incontinence occurs when stool seeps out around the distal fecal mass and leaks when the pelvic floor is relaxed (e.g., sleep), with fatigue or attempts at flatus and is occasionally mistaken for diarrhea. Physical examination includes assessing the anal tone and presence of stool in the rectal vault by rectal examination. In patients with functional constipation, the rectal examination causes the child to react with acute fear and negative behaviors.
In such a situation, examination of the perineum is important, and digital examination may be deferred to facilitate a therapeutic alliance with the child.

A number of predisposing factors appear to be associated with the onset of functional constipation. Painful defecation is a crucial but often silent clue as a potential trigger for chronic fecal retention and fecal soiling. Toilet training is often a potential trigger. To master toilet training, a toddler must develop the interest and ability in retaining a bowel movement until it can be released into the toilet. This behavior often leads to less frequent defecation and, at times, hard painful stools. This problem may be exacerbated if toilet training is vigorously encouraged before the child is developmentally ready. The American diet is a potential contributor to chronic constipation. Although a balanced diet of fruits, vegetables, and fiber maybe useful in preventing mild constipation, there is little evidence that fiber alone is effective in the treatment of chronic constipation.

Regardless of the etiology, once constipation is triggered, a positive feed-backtype mechanism ensues. Retained stool in the distal colon begins to lose water across the intestinal wall. As water is resorbed, fecal motility slows, more water is lost, and the feces harden. A buildup of desiccated stool causes painful defecation that leads to ongoing stool retention. Over time, the rectum and distal colon accommodate the growing fecal mass and, consequently, the rectosigmoid enlarges. Under these conditions, a child’s ability to sense rectal fullness diminishes, and he or she may not appreciate the need to defecate. A classic sign of chronic constipation is the large, infrequent (up to 1 week or more) stool that clogs the toilet. The passage of hard stools frightens the child and results in fearful determination to avoid defecation. Such children respond to the urge to defecate by contracting the anal sphincter and gluteal muscles, attempting to withhold. Encopresis, or involuntary fecal soiling, is for all families a source of tremendous stress. It is a complication of severe functional constipation that occurs when watery stool from the proximal colon leaks around the fecal obstruction, passing involuntarily per rectum. Parents or caretakers may misinterpret encopresis as diarrhea. Severe constipation may also lead to rectal prolapse.