Formula Medical Group
Apple Valley, CA

James Krider, MD

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Hives or wheals - urticaria

Hives are red, itchy, swollen patches that form on the skin. They typically start as small, raised bumps that swell and produce pink or red lesions called wheals. Wheals have clearly defined edges and flat tops, and they often join together quickly to form larger areas of raised, red or skin-colored lesions called plaques. Wheals and plaques can appear suddenly, change shape, disappear, and reappear over the course of a few minutes or up to several hours.

Hives usually are part of an allergic skin response, often due to an adverse reaction to a food or drug. An over reaction of the body's immune system triggers the response. As part of this allergic response, chemicals called histamines are produced, and these substances cause the hives. Such allergic reactions range from mild and annoying to dangerous and life threatening. Hives are often accompanied by itching or other allergy symptoms.

Not all hives are related to allergies; sensitivity to cold, heat, water, or sunlight may also cause them, as can anxiety or stress.

Causes of hives or wheals

Food allergies
Hives are the most common allergic skin reaction to some foods. A variety of other symptoms may also occur, including nausea, abdominal pain, diarrhea, vomiting, difficult breathing, sneezing, and red, itchy eyes. In some people, only a minute amount of the offending food triggers hives, whereas others have a certain threshold of tolerance, experiencing symptoms only when surpassing this threshold. Some people react immediately and violently, while others have a delayed allergic response of several hours or even a few days. Among the foods most likely to cause allergic reactions are milk, fish, shell­fish, nuts, berries, eggs, chocolate, corn, wheat flour, lima beans, peanuts, and citrus and other fresh fruits.

Insect bites
A bite or sting by a bee, wasp, hornet, yellow jacket, and some ants injects venom into the body, which normally causes momentary pain followed by redness, irritation, and itching at the location of the bite. A

Instead of flat hives, some skin allergies produce fluid-filled blisters.
Instead of flat hives, some skin allergies produce fluid-filled blisters.

Hives or wheals begin small, but can swell to become large, red lesions called plaques.

Hives or wheals begin small, but can swell to become large, red lesions called plaques.

person who is hypersensitive or allergic to insect bites may develop other symptoms, including hives. A severe allergic reaction to insect venom varies from person to person, and may include dizziness, headaches, extreme nausea, and itching. Difficulty in breathing, hives, and swelling are important warning signs of a possible anaphylactic reaction, which requires emergency treatment to prevent shock and respiratory collapse.

Almost every drug has the potential to cause hives in susceptible persons. The same drug may cause different reactions in different people, or in the same person at different times or with different doses. Sensitivity to a drug usually increases as the dose is increased, but even a small amount of the drug can produce serious symptoms in a person who is hypersensitive to it.

In a few cases, the person may have an anaphylactic response. The reaction begins within minutes after the drug is administered, with the appearance of hives usually the first sign. This is rapidly followed by intense itching, runny nose, wheezing, paleness, cold sweats, low blood pressure, and difficulty in breathing as the larynx swells. Without prompt treatment, shock, coma, and cardiac arrest can occur.

Penicillin is one of the drugs that most commonly causes an allergic reaction. People who are allergic to penicillin or other antibiotics will often have a similar response to chemically similar drugs, so caution is needed in taking any medication. Some people develop a condition called serum sickness in response to certain medications. This type of reaction usually starts days to weeks after the drug is taken and may consist of hives, swelling of various parts of the body, fever, joint pain

and swelling, and enlarged lymph glands.

Each person reacts differently to stress. Some thrive on it, while others suffer a variety of physical and emotional symptoms, including breaking out in itchy hives.

Sun sensitivity
Exposure to sunlight causes hives in people who are photosensitive. The problem can be exacerbated by sweating or the use of medications such as tranquilizers, antidepressants, and diuretics, all of which promote sun sensitivity. Many skin medications, especially antiacne drugs that contain vitamin A, also cause hives and other reactions after exposure to sunlight. Babies' skin is often sun sensitive, and many develop a type of prickly heat accompanied by hives.

Advice about hives or wheals

Seek immediate medical care if the following symptoms of a possible anaphylactic reaction occur during an episode of hives:

  • Difficulty breathing or a tight or constricted feeling in the throat.
  • Wheezing.
  • Widespread swelling, especially of the mouth and throat.

To avoid future episodes of hives, try to:

  • Identify the cause, and then avoid it.
  • Never take any medication that has not been prescribed for you, especially if you have a history of drug allergies.
  • If you are prone to develop hives, don't wear tight underclothing, since any skin irritation may trigger new outbreaks. Avoid hot baths and showers, and use cold water compresses or soaks to relieve itching.
  • Decrease strenuous physical activities until several days after hives disappear. Avoid getting hot and sweaty.
This article was last reviewed November 12, 2005 by Dr. James Krider.
Reproduced in part with permission of Home Health Handbook.
Allergic reactions, skin
Allergies, food
Allergies, anaphylaxis
Anaphylactic shock
Bee-sting hypersensitive
Insect bites
Med's, antibiotics

Med's, skin
Prickly heat
Skin and hair
Sun sensitivity

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