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Hives, also known as urticaria, are itchy, raised welts that are found on the skin. They are usually red, pink, or flesh-colored, and sometimes they sting or hurt. In most cases, hives are caused by an allergic reaction to a medication or food or a reaction to an irritant in the environment.
In many cases, hives are an acute (temporary) problem that may be alleviated with allergy medications. Most rashes go away on their own. However, chronic (ongoing) cases, as well as hives accompanied by a severe allergic reaction, are larger medical concerns.
Hives are usually caused by an allergic reaction to something that you have encountered or swallowed. When you have an allergic reaction, your body begins to release histamines into your blood. Histamines are chemicals your body produces in an attempt to defend itself against infection and other outside intruders. Unfortunately, in some people, the histamines can cause swelling, itching, and many of the symptoms that are experienced with hives. In terms of allergens, hives can be caused by factors such as pollen, medications, food, animal dander, and insect bites.
Hives might also be caused by circumstances besides allergies. It’s not uncommon for people to experience hives as the result of stress, tight clothes, exercise, illnesses, or infections. It’s also possible to develop hives as the result of excessive exposure to hot or cold temperatures or from irritation due to excessive sweating. As there are several potential triggers, many times the actual cause of hives cannot be determined.
People who are known to have allergies are more likely to get hives. You may also be at risk to develop hives if you are on medication or if you are unknowingly exposed to things you may be allergic to, such as food or pollen. If you are already ill with an infection or a health condition, you may be more vulnerable to developing hives.
The most noticeable symptom associated with hives is the welts that appear on the skin. Welts may be red, but can also be the same color as your skin. They can be small and round, ring-shaped, or large and of random shape. Hives are itchy, and they tend to appear in batches on the affected part of the body. They can grow larger, change shape, and spread.
Hives may disappear or reappear over the course of the outbreak. Individual hives can last anywhere from half an hour to a day. Hives may turn white when pressed. Sometimes the hives may change shape or form together and create a larger, raised area.
Hives can occur in a variety of places on the body. Call 911 or seek medical attention immediately if you develop a hive outbreak around your throat or on your tongue or have trouble breathing along with hives.
The most common causes of hives are allergic reactions. These can be caused by any allergen you might be sensitive to, including:
Mild cases of hives caused by allergies are typically treated with long- or short-term allergy medications and avoidance of the trigger.
Anaphylaxis is a severe, life-threatening allergic reaction. In this condition, hives are often accompanied with breathing difficulties, nausea or vomiting, severe swelling, and dizziness. Call 911 immediately if you suspect anaphylaxis.
Chronic hives are ongoing cases that don’t necessarily have an identifiable cause. Also called chronic urticaria, this condition is marked by recurring hives that can interfere with your lifestyle. According to the Mayo Clinic, these can last between six weeks and several months or years.
You may suspect chronic hives if you have welts that don’t go away within six weeks. While not life-threatening, this form of hives can be uncomfortable and difficult to treat. They may also be a symptom of an underlying health problem, such as:
This form of acute hives is considered mild. Excessive scratching or continuous pressure on the skin causes it. Dermatographism usually clears up on its own in a short period of time without treatment.
Sometimes changes in temperature can induce hives in people who are sensitive to such changes. Cold-induced hives may occur from cold water or air exposure, while body heat from physical activity may cause exercise-induced hives. Exposure to sunlight or tanning beds may also bring about solar hives in some people.
Both viral and bacterial infections can cause hives. Common bacterial infections causing hives include urinary tract infections and strep throat. Viruses that cause infectious mononucleosis, hepatitis, and colds often cause hives.
The first step in getting treatment is to figure out if you actually have hives. In most cases, your doctor will be able to determine if you have hives from a physical exam. Your skin will show signs of the welts that are associated with hives. Your doctor may also perform blood tests or skin tests to determine what may have caused your hives — especially if they were the result of an allergic reaction.
You may not need prescription treatment if you’re experiencing a mild case of hives not related to allergies or other health conditions. In these circumstances, your doctor might suggest that you seek temporary relief by:
Anaphylaxis is a medical emergency that needs to be treated immediately by a physician.
Simple changes to your lifestyle may be able to help you prevent hives from reoccurring in the future. If you have allergies and you know which substances are likely to cause an allergic reaction, your doctor will suggest that you avoid any possible exposure to these factors. Allergy shots are another option that may help you reduce the risk of experiencing hives again.
Avoid being in high-humidity areas or wearing tight clothing if you have recently had a hives outbreak.
Although hives can be itchy and uncomfortable, usually they are not severe and will disappear after a period of time. However, be aware that as some hives go away, new ones may pop up.
Mild cases of hives are considered harmless. Hives can be dangerous if you are having a serious allergic reaction and your throat is swelling. Prompt treatment for a severe case of hives is important for a good outlook.
Written by: The Healthline Editorial Team
Medically reviewed on: May 18, 2017: Sarah Taylor, MD
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