Urticaria, commonly known as hives, is a frequent skin reaction characterized by the sudden appearance of raised, itchy welts. These welts, which can be red or flesh-colored, result from a temporary swelling of the skin’s surface. Hives can appear anywhere on the body, varying greatly in size. Approximately 20% of people will experience hives at some point in their lives. The condition is generally temporary, with individual welts typically lasting less than 24 hours before fading without a trace.
Why Hives Are Not Contagious
Hives are an internal immune system response, meaning the rash cannot be passed from person to person. They are not caused by an external infectious agent like a virus, bacteria, or fungus. Hives occur when specialized skin cells, called mast cells, release chemical mediators, most notably histamine. This histamine causes small blood vessels in the skin to widen and leak fluid into the surrounding tissue, creating the characteristic raised, swollen welts, or wheals. Because this reaction is localized within an individual’s body, it is non-transmissible.
It is possible for a contagious infection, such as a cold or strep throat, to trigger a hives breakout. In these cases, the infection is what is transmissible, but the hives themselves remain a non-contagious side effect of the underlying condition.
Understanding Common Hives Triggers
Hives are triggered by a wide range of factors that activate the mast cells to release histamine. These triggers are broadly categorized as either allergic or non-allergic, and often the exact cause remains unknown. Allergic triggers involve the immune system reacting to a specific substance it mistakenly identifies as a threat.
Common examples include specific foods like peanuts, shellfish, or eggs, as well as certain medications such as antibiotics, aspirin, or ibuprofen. Insect stings and latex are also known allergic triggers.
Non-allergic triggers, sometimes called physical urticaria, involve a direct physical stimulus to the skin. These can include environmental factors such as exposure to cold temperatures, heat, water, or sunlight. Hives may also be induced by physical pressure, like that from tight clothing or vibration. Emotional stress or vigorous exercise can also cause hives by triggering an increase in body temperature.
Telling Hives Apart from Contagious Rashes
Distinguishing hives from contagious skin conditions often comes down to the appearance and behavior of the rash. Hives are defined by welts that are transient, meaning an individual welt typically disappears within 24 hours, though new ones may appear elsewhere. If you press on a hive, the center of the welt will temporarily turn white (blanching), indicating the swelling is caused by fluid in the skin. The welts are raised and smooth, and they do not present with blistering, flaking, or crusting.
Contagious rashes display different characteristics. Chickenpox, for instance, develops into fluid-filled blisters that eventually scab over. Impetigo is a bacterial infection that typically results in sores that ooze and form a characteristic yellowish or honey-colored crust. Ringworm, which is a fungal infection, presents as a scaly, ring-shaped patch with clear borders, unlike the individual, shifting welts of hives.
Contagious infections that cause a rash, such as measles or scarlet fever, are often accompanied by systemic symptoms like a high fever, body aches, or general malaise. In contrast, simple acute hives, especially those caused by an allergic reaction, are usually limited to the skin and do not cause these widespread signs of illness.
Immediate Care and When to See a Doctor
For mild cases of hives, immediate care focuses on alleviating the intense itching and swelling. Over-the-counter H1 antihistamines, such as cetirizine or loratadine, are the first-line treatment as they block the effects of histamine and help reduce the rash. Applying cool compresses or taking a cool bath can also provide localized relief from itching and discomfort. Avoiding known triggers, such as hot showers or tight clothing, can prevent recurrence.
It is important to seek immediate emergency medical attention if hives are accompanied by signs of a severe allergic reaction, known as anaphylaxis. These symptoms indicate that the swelling is affecting areas beyond the skin. Signs include swelling of the tongue, lips, or throat (angioedema), difficulty breathing, wheezing, dizziness, or a sudden drop in blood pressure. Anyone experiencing these symptoms requires prompt treatment with an epinephrine auto-injector, if available, and emergency medical services should be called immediately.