Most people never pinpoint the source, and in many cases, it is unnecessary anyway. Hives often erupt suddenly and clear just as quick as they appeared, never to bug you again. However, if they are persistent, severe, or frequently bothersome, finding a cause can be critical for your comfort.
Some people release histamines and develop hives from physical or environmental stimulation to their skin. If you have this condition, stimuli like hot or cold temperatures, pressure against the skin, exercise, sunlight, or even water may lead to uncomfortable and itchy skin. This type of urticaria is called inducible or physical urticaria.
Localized allergic hives are usually due to your skin contacting a trigger, like a patch on your ankle where the dog licked you. Widespread allergic hives are more likely due to an allergic reaction to an ingested food or medication. Sometimes the cause is apparent. However, you may need to undergo testing if you cannot identify a reason for your rash.
Hives resulting from an allergy require you to find your triggers and avoid them. Your doctor can order specific blood tests or allergy skin testing to discover the culprit. A blood test looks for antibodies your immune system produces specifically to common allergens. A skin test exposes your skin to known allergies, followed by an examination to look for reactions.
If your hives are chronic, your doctor may want to investigate the possibility of an autoimmune disease. Autoimmune diseases are conditions in which your immune system attacks healthy tissue mistaking it as foreign and can lead to skin reactions. You may need to provide a blood sample for laboratory testing, so your healthcare provider can gather information about your overall health.
Allergic reactions to medicines can occur with any drug, including herbal supplements. If you experience hives after ingesting medications, there is a possibility it is due to an allergy. Drug allergies can generate severe and life-threatening reactions. If you break out in a rash after taking medication, even if symptoms are minimal, contact your doctor. If you experience a severe reaction, seek immediate medical help.
Viral or Bacterial Infections
Viral infections are a common cause of hives, especially in children. In one study evaluating urticaria in kids between the ages of 1 and 19, almost half with acute urticaria had a documented infection. During an illness, the immune system can become overly excited about fighting off a pathogen and signals for mast cells to release histamines.
Types of Hives
Hives come in different varieties and different classifications. There are two main types, acute and chronic. Grouping them into categories allows for a more straightforward diagnosis and treatment. If your doctor knows what kind you have, they can tailor a plan to manage your condition.
Acute urticaria, or acute hives, last six weeks or less, appears suddenly, and often passes without trouble. This type is usually due to an allergy or infection. You might experience acute hives when something you are allergic to contacts your skin or from ingesting certain foods or medicines. Certain pathogens, usually viruses, can also make your skin breakout.
When your hives last longer than six weeks, they shift away from acute and move into the chronic category. Chronic urticaria can flare up daily and may last months or even years. Most cases exist without a known cause.
Chronic urticaria is broken down into two main types, inducible and spontaneous. Inducible chronic hives are initiated by physical stimuli like heat, pressure, or sun exposure. If your hives are not inducible, they are considered spontaneous.
Chronic urticaria can result from an autoimmune disease or long-term infection. However, if there is no identifiable cause, you have chronic spontaneous urticaria. Most cases remain a mystery with no known cause.
Inducible (or Physical) Urticaria
Inducible urticaria is a type of chronic urticaria that occurs from environmental stimulation of the skin and comes in several different forms. The kinds of inducible urticaria are:
Dermographism is a type of urticaria that occurs when the skin breaks out in hives after being scratched, stroked, or mechanically irritated. Irritation from scratchy clothing or even a slight scratch from bumping your arm can result in red and aggravated skin.
Exercise-induced urticaria occurs after physical exertion, sweating, or sustained activity. It usually comes on suddenly and resolves quickly. In severe cases, exercise-induced anaphylaxis can occur.
Delayed-pressure urticaria is characterized by eruptions of hives after sustained pressure on the skin. Your hands, soles of your feet, buttocks, and areas under tight belts or bra straps are most frequently affected.
Cold-induced urticaria is a skin reaction to cold exposure. Welts can be mild to severe and appear within minutes after exposure. You may notice hives on your hands after holding cold items or swelling of your lips when you consume cold food or drink. Even cold air can lead to eruptions.
Cholinergic urticaria is a rash associated with an increase in body temperature. Anything that raises your temperature can cause hives with this type of urticaria. Fevers, feeling anxious, or taking a hot bath can trigger your body to release histamines, resulting in hives.
Aquagenic urticaria is an extremely rare form of hives where your skin reacts to water regardless of temperature or source. Rain, showers, swimming, or even touching water to wash your hands can stimulate hypersensitive mast cells and irritate your skin. As of 2018, only 50 cases have been reported in the medical literature.vi
Solar Urticaria is a rare photosensitivity disorder where your skin reacts to sun exposure. The reaction is usually sudden and can appear from just a few minutes in the sun. In more severe cases, the hives can turn into blisters.
Chronic Spontaneous Urticaria
Chronic spontaneous urticaria is a condition in which you experience hives lasting beyond six weeks with no identifiable etiology or known cause. You may, however, detect circumstances that aggravate your symptoms. The rash can come and go daily but exists most days of the week. Although eruptions can appear anywhere on your body, you'll likely observe specific areas that tend to be more affected.
There are no laboratory or clinical tests available to diagnose this condition. Your doctor must rely on signs and symptoms while eliminating other potential causes to reach a diagnosis. Once diagnosed, your doctor can help you manage your hives even without knowing the origin. In 80% of cases, symptoms resolve without treatment within two to five years.
Angioedema Versus Hives
Urticaria and angioedema share similar triggers and occur together in 49% of cases. They are both an overreaction of the immune system and are usually self-limited. Although there are many commonalities between urticaria and angioedema, they present differently.
Hives affect the superficial layers of the skin with itchy welts that have a rash-like appearance and somewhat clear borders. Angioedema involves deeper layers of skin and presents as localized tissue swelling. Angioedema is rarely itchy but can burn and feel uncomfortable, which is also sometimes seen with hives.
Angioedema can affect anywhere on the body, including your intestines. If your intestines are involved, you may notice digestive problems like abdominal pain, diarrhea, nausea, and vomiting. You can also suffer from swelling in your hands, feet, genitals, or face, including your lips and tongue. In severe cases, you may feel dizzy or faint due to changes in blood pressure.
Swelling in your tongue or throat can obstruct your airways and make breathing difficult. Seek immediate medical attention if your angioedema affects your ability to breathe. If you feel dizzy, lose conciseness, or have difficulty breathing, it is a medical emergency. Call 911 or go to the nearest emergency department straight away.