What Are Hives?

Hives are red raised bumps or welts on the skin. Hives (or urticaria) is a common skin reaction to something like an allergen (a substance that causes allergies).

The spots can appear anywhere on the body and can look like tiny little spots, blotches, or large connected bumps.

Individual hives can last anywhere from a few hours to a week (sometimes longer), and new ones might replace those that fade. Hives that stay for 6 weeks or less are called acute hives; those that go on longer than 6 weeks are chronic hives.

What Causes Hives?

An allergic reaction can cause hives, as can:

• temperature extremes
• stress
• infections
• some illnesses

In some cases, a person has hives and angioedema, a condition that causes swelling around the eyes, lips, hands, feet, or throat. Very rarely, hives and angioedema are associated with an allergic reaction that involves the whole body or anaphylactic shock.

The red welts of hives happen when mast cells in the bloodstream release the chemical histamine, which makes tiny blood vessels under the skin leak. The fluid pools within the skin to form spots and large welts. This can happen for a number of reasons. But in many cases the cause is never found.

Most often, hives are associated with an allergic reaction, which can make the skin break out within minutes. Common allergies include:

• foods, especially shellfish, peanuts, tree nuts, milk, and fruit
• medicines (antibiotics) and allergy shots
• pets and other animals
• pollen
• insect bites and stings

Sometimes a breakout of hives has nothing to do with allergies. Other causes include:

• infections, including viruses
• exercise
• anxiety or stress
• sun exposure
• exposure to cold, such as cold water or snow
• contact with chemicals
• scratching (dermatographia)
• putting pressure on the skin, such as from sitting too long or carrying a heavy backpack over a shoulder

Hives due to physical causes (such as pressure, cold, or sun exposure) are called physical hives.

It can be hard to figure out what causes chronic hives, though it's sometimes linked to an immune system illness, like lupus. Other times, medicines, food, insects, or an infection can trigger an outbreak. Often, though, doctors don't know what causes chronic hives.

What Are the Signs & Symptoms of Hives?

The hallmark red raised welts are the main sign of hives. The welts can:

• have a pale center
• appear in clusters
• change shape and location in a matter of hours
• be tiny or as big as a dinner plate
• itch, sting, or cause a burning sensation

Someone who also has angioedema might have puffiness, blotchy redness, swelling, or large bumps around the eyes, lips, hands, feet, genitals, or throat. Other symptoms can include nausea, vomiting, or belly pain.

Rarely, a person with hives and angioedema can also get anaphylactic shock. Signs of anaphylactic shock include breathing trouble, a drop in blood pressure, dizziness, or a loss of consciousness (passing out).

How Are Hives Diagnosed?

Most of the time, a doctor can diagnose hives just by looking at the skin. To find the cause, you may be asked questions about your medical history , recent illnesses, medicines, exposure to allergens, and daily stressors.

If you have chronic hives, the doctor may ask you to keep a daily record of activities, such as what you eat and drink, and where the hives tend to show up on your body. Diagnostic tests — such as blood tests, allergy tests, and tests to rule out conditions that can cause hives, such as thyroid disease or hepatitis — might be done to find the exact cause of the hives.

To check for physical hives, a doctor may put ice on your skin to see how it reacts to cold or place a sandbag or other heavy object on your thighs to see if the pressure will cause hives.

How Are Hives Treated?

In many cases, mild hives won't need treatment and will go away on their own. If a definite trigger is found, avoiding it is part of the treatment. If the hives feel itchy, the doctor may recommend an antihistamine medicine to block the release of histamine in the bloodstream and prevent breakouts.

For chronic hives, the doctor may suggest that you take a non-sedating (non-drowsy) prescription or over-the-counter antihistamine every day. Not everyone responds to the same medicines, though, so it's important to work with the doctor to find the right one for you.

If a non-drowsy antihistamine doesn't work, the doctor may suggest a stronger antihistamine, another medicine, or a combination of medicines. In rare cases, a doctor may prescribe a steroid pill or liquid to treat chronic hives. Usually this is done for just a short period (5 days to 2 weeks) to prevent harmful steroid side effects.

In Case of Emergency

Anaphylactic shock and bad attacks of hives or angioedema are rare. But when they happen, they need immediate medical care.

People with bad allergies should carry an injectable shot of epinephrine . The doctor will teach you how to safely give yourself an injection if you are at risk for a severe allergic reaction.