Health Inquiry Responses

Dear Dr. Roach:

I hope this isn’t too trivial, but I’ve been pondering it for about 20 years. I’m a healthy 77-year-old man without any medical issues. Whenever I feel the need to have a bowel movement, I experience significant sweating in my buttocks. Once I finish, the sweating stops.

A while back, I asked my primary care doctor about this, but he didn’t have an explanation. I brought it up again at my last annual check-up, yet still nothing. I’m not necessarily looking for a solution—though I could use an antiperspirant, I’m not interested in that. I just want to understand why this happens. Can you shed some light on it?

— B.C.

Dear B.C.:

When you go to the bathroom, your body activates a part of the nervous system known as the “parasympathetic” system. You might recall that while the sympathetic system handles “fight or flight” responses, the parasympathetic system is more about “rest and digest.” It’s fairly common to experience excessive sweating during a bowel movement, sometimes referred to as “poop sweats.” In some cases, this response can even lead to fainting.

However, what’s a bit less typical is your specific case—where it seems concentrated around the buttocks. Some people experience generalized sweating all over, while others have what’s termed “focal hyperhidrosis,” where sweating is more localized, like on the face or hands.

So, it seems you have focal hyperhidrosis of the buttocks, triggered by the act of defecation. It’s an unusual but not entirely unheard-of physiological reaction to a standard neurological event.

Dear Dr. Roach:

I’ve been on a 75 mcg daily dose of Synthroid for a couple of years now. Back in January 2025, my thyroid-stimulating hormone (TSH) level was at 3.48 mU/L, but recently it shot up to 36.5 mU/L.

I was trying to pinpoint any lifestyle changes, and two stood out: I started taking fish oil and switched to steel-cut oatmeal for breakfast almost every day. I’ve noticed my skin is extremely dry, I’ve been constipated, and my mood has taken a downturn—I find myself crying easily, which is unusual for me.

I looked up the connection between oatmeal and thyroxine and found that they don’t interact well if consumed close together. Is that something you’ve heard about? Are there other foods I should steer clear of?

— M.M.

Dear M.M.:

I’m aware that beverages containing caffeine, particularly coffee, can negatively affect the absorption of thyroxine (like Synthroid). Milk can also cause reduced absorption, as can calcium supplements.

While there’s some mention of fiber supplements potentially impacting thyroxine absorption, the significance of this has been debated. It’s unusual that your TSH level has spiked so drastically.

A high TSH typically indicates low levels of thyroxine (T4) or triiodothyronine (T3). The combination you have—high TSH and low T4—suggests that your thyroid is not producing enough hormone, alongside possibly inadequate hormone replacement. The symptoms you describe align quite closely with this condition.

Although oatmeal, being high in fiber, may be a factor, I’d also want to rule out if you’ve been consuming coffee or milk around the time you take Synthroid. Checking any other medications that might interfere with absorption, like omeprazole, antacids, cholestyramine, or iron supplements, would be worthwhile.

Lastly, considering other causes of poor absorption, such as inflammatory bowel disease or celiac disease, might be beneficial, although your constipation makes those less likely.