DEAR DR. DONOHUE: I have a rash that has lasted for six months. It’s very itchy. The itchy spots are both large and small, and the itching lasts 15 to 20 minutes. I get them all over my body at different times, 24 hours a day. I have been on Zyrtec for three months, but it only controls so much. I also take Benadryl. I have been diagnosed with peanut allergy, so I carefully read labels to avoid them; it hasn’t helped. How long does it take for peanuts to leave the system? — J.S.

ANSWER: You describe chronic hives (urticaria) to a T. It’s recurrent outbreaks of itchy, red skin bumps that look a bit like mosquito bites. Chronic hives are crops of them that keep appearing for longer than six weeks. Although everyone immediately thinks this is an allergic reaction, allergy is the cause in only a few people. The mechanisms causing the outbreak are understood, but what turns those mechanisms on isn’t understood. Histamine and a host of similar body chemicals are released into the blood. Modern theory suggests that the release stems from an attack by the immune system on cells that produce those chemicals.

Many doctors check for food and drug allergies. Foods that are implicated the most are spices, herbs, eggs, seafood, smoked meats, tomatoes, peas, mushrooms, spinach, olives, breads and margarines. The most often blamed drugs include penicillin, sulfa, diuretics (water pills), aspirin, NSAIDs (Aleve, Advil, etc.) and ACE inhibitors (blood pressure medicines). Thyroid disease sometimes brings on hives. Although these things are not commonly found as causes of chronic urticaria, a search for them can be a huge help to the minority of cases in which they are playing a role.

Treatment centers on antihistamines taken on a regular basis, not just when an outbreak occurs. Zyrtec (cetirizine) is often chosen. Allegra, Claritin and Clarinex are other frequent choices. Benadryl and Atarax, two older antihistamines, are most useful when taken before bedtime. They’re sedating and can provide uninterrupted sleep.

On the bright side, most people get over chronic hives in one to two years. On the dark side is the fact that not all do.

DEAR DR. DONOHUE: I saw an article about a new kind of AIDS virus, called AIDS-2. It was alarming. It said this new virus could spread even more widely than the older virus. Is this just another example of fear-mongering? — T.R.

ANSWER: HIV-1, human immunodeficiency virus 1, is the major cause of AIDS. HIV-2 is a virus similar to HIV-1 that causes AIDS, usually to a lesser degree than does the HIV-1 virus. HIV-2 appears to have originated in the west coast of Africa. It’s not a new virus. It’s been known for many years. It’s treated with the same medicines used for HIV-1.

DEAR DR. DONOHUE: Ever since my teens, when I used to get many bloody noses, I have put a light coat of Vaseline on the lining of my nose at the entrance. I haven’t had any bloody noses since I started doing this.

People tell me this is a danger. It can cause pneumonia. Is this for real? — B.C.

ANSWER: A light coat of petroleum jelly (Vaseline) on the lining of the lower nose is not going to get you or anyone else in trouble. A huge glob of petroleum jelly might find its way into the lungs. That could cause what’s known as lipid pneumonia.

You can continue your practice without fear. It’s worked for you: You’re not having any more nosebleeds. A dry nasal lining is one cause of nosebleeds. The dried-out lining flakes off on the slightest pressure. Even lightly touching the nose can cause it to fall off and promote a nosebleed.

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 or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.