DEAR DR. DONOHUE: I don’t know if you ever heard of this, but I hope you have. My doctor thinks I’m making it up. When I work – vacuum, clean, scrub floors – I start itching and break out with a rash on my face and chest. I am not making this up. I feel the itch, and I can see the rash. When I see the doctor, I don’t have any symptoms. Do you have any idea what this might be? – R.M.

ANSWER: It could be cholinergic urticaria. The “cholinergic” part comes from acetylcholine, a chemical released by nerve cells. “Urticaria” is another word for hives.

Release of acetylcholine activates a special body cell, the mast cell, to release itch-causing, rash-provoking substances. Tiny, itchy hives pop out on the face, chest and abdomen. The hives are much smaller than ordinary hives, and you might see only red skin and not recognize the hives.

Exercise of any sort that raises body temperature can cause the outbreak. For some, a hot bath or shower or a fever triggers an attack. Even highly emotional situations, like an embarrassment or the anticipation of speaking in public, can set off an episode. The affair lasts from half an hour to an hour and a half.

A cool shower can put an end to an attack. So can antihistamines, which you can take in anticipation of an outbreak as a preventive measure. There are many antihistamines, and you have to experiment to find the one that suits you best. Cholinergic urticaria has no health significance. A few, however, develop asthma symptoms – wheezing, cough and difficulty breathing – during an attack.

DEAR DR. DONOHUE: What are your thoughts on taking a multivitamin? I take one for my personal health insurance and to prevent cancer. Cancer runs in our family. Is this smart? – N.C.

ANSWER: Vitamin supplementation is important in some instances. If people have pernicious anemia, they have to take supplemental B-12. Vitamin D is a vitamin in which many people, particularly older, housebound people and people who live in northern climates, are either on the verge of being deficient or are actually deficient. They could stand a daily dose of this vitamin. Vitamin D is also needed to prevent and treat osteoporosis.

Folic acid is needed by women prior to and during pregnancy to prevent certain fetal malformations like spina bifida.

Realization of this and supplementation of foods with this vitamin have decreased the incidence of such malformations. People with bona fide vitamin and mineral deficiencies need daily supplements. Widespread vitamin and mineral deficiencies are not common in Canada and the United States. If taking a multivitamin puts your mind at ease and if the cost of the vitamin is not prohibitive, then you’re not hurting yourself, and you might be helping.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him at P.O. Box 536475, Orlando, FL 32853-6475.