Hives

Hives, scientifically known as urticaria, are a common skin rash characterized by red or flesh-colored, raised bumps.

These bumps may itch intensely, or they might cause a stinging or burning sensation. Hives can appear anywhere on the skin's surface. They may be as small as a pinpoint or several inches in diameter. They can also appear as individual bumps or merge together into larger patches. Most cases are short-lived and do not leave lasting marks on the skin. However, if hives last for more than six weeks, the condition is called chronic urticaria.

The biological mechanism behind hives involves a complex inflammatory reaction. Inside the skin, there are specialized cells called cutaneous mast cells. When triggered, these cells release inflammatory mediators, including a substance called histamine. This release causes fluid to leak from superficial blood vessels in the dermis. This leakage creates the swelling, or edema, that forms the visible bumps.

A related condition is angioedema. In angioedema, the fluid leakage occurs from much deeper blood vessels in the subcutaneous or submucosal layers. While most hives are benign, urticarial vasculitis is a more serious condition. It is identified by hives that are painful, last over 24 hours, or leave a bruise during healing.

There are many different types of urticaria classified by their triggers. Dermatographic urticaria, or "skin writing," occurs when stroking or scratching the skin creates raised welts. This affects about 4% to 5% of the population. Another type is cholinergic urticaria (CU), which is provoked by sweating from exercise, bathing, or emotional stress. Cold urticaria is caused by exposure to extreme cold or damp conditions. This can manifest as a rare hereditary form or a common form on the face and hands. Solar urticaria appears on skin exposed to the sun, while aquagenic urticaria is triggered by contact with water.

Physical triggers can also include pressure and exercise. Pressure urticaria can occur immediately or as a deferred response about six hours after pressure is applied. This can be caused by tight clothing, belts, or sitting on hard surfaces. Exercise urticaria (EU) is a distinct condition first identified in 1980. People with EU experience hives, shortness of breath, and low blood pressure within five to 30 minutes of starting exercise. Jogging is a common trigger for this condition. In some cases, EU only occurs if a person exercises within 30 minutes of eating specific foods like wheat or shellfish.

Understanding the causes of hives involves looking at various environmental and biological agents. Many people experience hives due to allergic reactions to medications, such as penicillin, aspirin, or ibuprofen. Food allergies are also common; shellfish and nuts are frequent triggers for adults, while eggs, wheat, and soy are common in children. Some people may even have an alpha-gal allergy, causing sensitivity to red meat and milk. Infections, such as those caused by Streptococcus or certain parasites, can also trigger hives. In over 50% of chronic cases where the cause is unknown, an autoimmune reaction is likely responsible.

History shows that humans have recognized hives for millennia. The condition has been described since at least the time of Hippocrates. The medical term urticaria is derived from the Latin word "urtica," which means nettle. This name reflects the stinging sensation similar to touching a nettle plant. Approximately 20% of the population will experience hives at some point in their lives. While short-duration cases affect males and females equally, long-duration cases are more common in females. Short-duration cases are more common in children, whereas long-duration cases are more frequent in middle-aged individuals.

Treatment and prevention depend heavily on identifying the specific trigger. The primary method of prevention is avoiding the substance or agent that causes the reaction. Doctors often use patch testing to help identify specific allergies. For most people, antihistamines are the preferred treatment. Second-generation antihistamines, such as fexofenadine, loratadine, and cetirizine, are often chosen because they carry a lower risk of sedation. In stubborn or refractory cases, doctors may prescribe corticosteroids or leukotriene inhibitors. For chronic cases lasting over six weeks, long-term antihistamine therapy or immunosuppressants like omalizumab may be required.