DEAR DR. ROACH: In the winter, I enjoy an occasional soak in a hot bath, especially when my muscles ache after a hard day, and I often add a cup or more of Epsom salts. These seem to make the bath even more soothing and therapeutic, and I feel especially clean afterward.

Am I crazy, or is there something to this? I’m wondering about the chemistry. Are these salts absorbed through the skin, and if so, isn’t a cup of salt rather harmful? And can they cause kidney stones? I had one of those last year and wonder if this had anything to do with it. — J.G.

ANSWER: Magnesium sulfate (Epsom salt) is used by many people as a soak and for purported health benefits. Many people feel that they make the bath especially relaxing. While magnesium is a critically important salt, we get the magnesium we need through food nearly all the time, while magnesium supplementation is necessary on occasion, such as in people taking certain diuretics.

However, although there may be some small absorption, magnesium is not at all well-absorbed through the skin, so there is neither harm nor benefit to soaking in Epsom salts. A cup is a commonly recommended amount of Epsom salt to add to a bath.

Sodium chloride (table salt) definitely increases the risk of kidney stones when taken by mouth, but magnesium does not. You can enjoy your Epsom salt bath without fear.

DEAR DR. ROACH: At 63, I’m familiar with age-related loss of elasticity, most noticeably with my skin. I’ve assumed that it was occurring all throughout my body. I hadn’t really worried about having to urinate three or four times a night; I had just assumed that my bladder didn’t stretch like it used to. I have been trying to hydrate more, as I do during the day with meals. I thought it was just my body continuing to process fluids into the night. Is three or four times a night really a red flag? — P.H.

ANSWER: Urinating frequently at night is common and can have several different reasons, only some of which are concerning. Inability of the bladder to stretch is not a common cause.

In men, it can be a symptom of prostate enlargement. Since the urethra, which empties the bladder, goes straight through the prostate, enlargement of the prostate can slow down urinary flow and make it more difficult for men to empty their bladder. Urinating small to medium amounts of urine several times a night is classic for prostate enlargement that isn’t due to cancer. Severe prostate enlargement can obstruct the kidney enough to cause damage on occasion, so it’s worth an evaluation.

In both men and women, overactive bladder (an involuntary spasm of the muscles in the bladder) can cause frequent urination, both during the day and at night. The symptoms for OAB are many small voidings, and it sometimes may cause incontinence. OAB and prostate enlargement can be hard to tell apart in men.

Men and women who have many large voids at night are getting rid of excess fluid. This could be because you just drank a lot of fluid before bed, so don’t do that. I recommend to stop drinking at 5 or 6 p.m. It can also be due to diabetes and sometimes kidney or heart failure. There are less common causes, so it really is worth speaking to your doctor about this issue.

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