The Itch of Which We Do Not Speak

Have an itch down there? Dietary triggers may be to blame.

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In this Age of Oversharing, topics previously considered social taboos have become acceptable fodder for conversation. From intimate details broadcast on Facebook news feeds to celebrity "TMI" – yes, I’m taking about you, Michael Douglas – it seems that no conversation topic is off limits these days. 

There does, however, remain at least one subject with a stigma that appears to be alive and well. We can refer to it by its polite Latin name, pruritus ani, or by the endearing term that the British use to describe it: “itchy bottom.” Translated into layman’s terms, it is chronic anal itching, usually accompanied by an uncontrollable urge to scratch. 

Pruritus ani is a complaint I encounter quite frequently in my clinical practice, although most of my patients only mention it as a casual aside, once they’ve become comfortable with me. Understandably, people find the condition to be embarrassing, and as a result, many do not readily seek out help. But pruritus ani is more common than you’d think: It affects 1 to 5 percent of adults. It's also more common in men than in women.

[See: Top Recommended Hemorrhoidal Preparations.]

There are more than a hundred documented causes of pruritus ani, and usually a gastroenterologist or proctologist is the most experienced person to evaluate and treat the condition. But if a medical condition is not the apparent culprit, a dietary trigger may be causing the itchiness. It’s important to realize that, unlike the preceding length of the digestive tract, the anus is lined with skin that contains all the same nerve endings as skin found elsewhere on the body. This highly sensitive skin, however, is situated directly in the fecal stream. Therefore, dietary components that affect the composition of the stool or impact the frequency of bowel movements can provoke unpleasant sensations of itchiness or pain in the anal tissue. Here are some such examples:

Alcohol use and smoking: Besides being a general irritant to the lining of the digestive tract, alcohol – particularly beer and wine – can acidify the stool as the result of its fermentable carbohydrate content. (See more about this phenomenon below.) More acidic stool can be irritating to sensitive anal tissue, much in the same way that sensitive skin anywhere on the body might be irritated if subjected to contact with an acidic substance. The fact that alcohol can also increase colonic motility – and therefore result in more frequent bowel movements – only adds to the contact, and consequently, the trouble.

[See: Top Recommended Diarrhea Treatments.]

It is unclear what mechanism underlies smoking’s role in exacerbating pruritus ani. Some experts propose that nicotine, a compound that stimulates motility in the colon, may increase the passage of stool over already inflamed anal tissue, thus worsening the sensation of itching in already affected individuals. Another possibility is that nicotine may contribute to anal sphincter muscle spasms, which can be perceived as itchiness. In either event, as if you needed another reason to quit smoking, tobacco is not your friend when you suffer from pruritus ani.

Caffeine: Caffeine bears a chemical resemblance to a compound called adenosine, a neurotransmitter with an inhibitory effect on various nervous system functions. When caffeine – a stimulating neurotransmitter – outcompetes adenosine for its receptors, it can stimulate free nerve endings in an itchy or painful way. In sensitive individuals, avoiding caffeine from coffee, soda and teas may be helpful in alleviating pruritus ani.

Carbohydrate malabsorption, such as lactose or fructose intolerance:  When sugars are not absorbed in the small intestine, they continue to travel intact to the colon where they are greeted by a teeming – and hungry – community of bacteria. Among the local residents are various species of friendly bacteria –  such as lactobacilli and bifidobacteria –who are happy to ferment those unabsorbed carbs. A byproduct of their fermentation is lactic acid, which shows up in the stool. Increased levels of lactic acid in the stool lower its pH and may be irritating to the delicate tissue of the anus when passing through. As a result, people who are lactose or fructose intolerant may experience anal itching or burning several hours after consuming lactose or fructose, respectively, at levels beyond their individual levels of tolerance. In these cases, following a low-lactose or low-fructose diet may help resolve the itchiness, although barrier ointments can also be helpful.

[See: Top Recommended Lactose Intolerance Medicines.]

The occasional spicy meal: It’s a funny thing how our body economizes when it comes to sensory receptors. The receptors that transmit sensations of itch and pain in our digestive tract moonlight as receptors that transmit sensations of spiciness when they encounter capsaicin, the compound responsible for the burning heat in chili peppers. When these shared receptors are saturated with spicy stimuli from, for example, daily intake of hot sauce, capsaicin tablets or even topical capsaicin creams, they are less able to respond to competing stimuli of itch or pain. Conversely, when exposure to spicy foods is inconsistent and infrequent, a sporadic encounter with capsaicin may actually trigger uncomfortable sensations of itchiness or pain at the far end of the GI tract. 

If you find that spicy foods give your bottom grief, you can try to rectify the problem in one of two ways: Avoid spicy foods entirely, or commit to taking a daily dose of capsaicin to keep your itch receptors bathed in distracting spicy stimuli. If the latter approach is of interest, I often recommend a daily (or nightly) Virgin Mary: tomato juice spiked with a teaspoon of Tabasco sauce. A daily capsaicin supplement may also be an effective alternative. Some doctors may prescribe a capsaicin-containing topical cream to similar effect.

If itchy bottom plagues you despite eliminating the most obvious dietary triggers, don’t be shy to seek professional help. While the most common causes are relatively minor conditions such as hemorrhoids or anal fissures, in some cases that itch can be a sign of something more serious, like anal cancer. While it’s understandably awkward to bring up your itchy affliction at Thanksgiving dinner, pruritus ani is a perfectly acceptable topic of conversation in the privacy of an exam room with your doctor.  

[Read: 5 Tips for a Smooth Doctor's Visit.]