DEAR DR. ROACH: I get horrible fever blisters when I go on any tropical vacation and am exposed to lasting sun. These blisters develop on my lower lip. I have tried sunscreen, but nothing has worked. On my most recent trip, the blisters appeared on the final day and took nearly three weeks to heal. It’s painful and horribly embarrassing. Is there anything I can do? Should I see my dermatologist? — S.A.

ANSWER: The sun can cause many kinds of skin reactions. In some people, the light itself causes the problem (these reactions are called photodermatoses). In others, the sun causes a reaction in combination with exposure to a particular substance. Sometimes, it’s a fruit, especially limes. In people with blisters around the mouth, I think of mangoes, especially if you are enjoying them in the tropics.

Some skin diseases just get worse in the sun: Lupus is the classic example, but there are many others (my textbook lists about 50, some quite rare).

A dermatologist is indeed the person to see. In the meantime, wear sun-protective clothing on your next tropical vacation, and consider a blocking sunscreen like zinc oxide in the areas where the blistering has occurred in the past.

DEAR DR. ROACH: My doctor recommends a tonsillectomy based on the fact that I suffer from chronic strep. I am apprehensive about this surgery as an adult. What are the realistic risks of the surgery versus continuing to experience regular cases of strep throat? — O.C.

ANSWER: Strep throat infections that are chronic (lasting more than three months) or recurrent are indications for tonsillectomy in adults; however, this is an uncommon surgery in adults, and there isn’t a lot of published data on the effectiveness of treatment. Some data show that tonsillectomy does reduce incidence of infection, as would be expected. Other data show improved quality of life and fewer missed work days.

My own experience is limited to a handful of patients: All have had significant improvement in the number and severity of infections. On the other hand, the surgery itself is unpleasant, and that’s putting it mildly. There is a significant risk of major complications (perhaps around 3 percent). One patient told me that the first two weeks after surgery were horrendous, but gradually improved over time.

As always, it’s a balance between benefits and risks of surgery. But it’s a difficult enough surgery that you are wise to be apprehensive, and I would recommend surgical consultation only if your symptoms were severe enough and significantly impact your life.

DEAR DR. ROACH: Three years ago, my mother was prescribed 50,000 IU of vitamin D per week. I read that this dose can lead to serious complications if continued for more than a month or two. How common is it for someone to be on such a high dose for three years? Should my mother insist that her doctor take her off this medication? — L.H.

ANSWER: Fifty thousand units a week is frequently given for eight to 12 weeks in people with significant deficiency in vitamin D, and people often then are switched to a daily dose of 1,000 to 2,000 IU. However, some people prefer a weekly dose, and 10,000 to 20,000 would be the usual dose.

Perhaps 10 to 20 percent of the time, in my experience, people do need higher doses, and 50,000 is not unheard of (some people have a genetic condition requiring high doses). However, this dosing should be guided by blood levels, and I certainly would feel better knowing that your mother has had her level measured if continuing this high dose.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from www.rbmamall.com.