Rash

A rash is a visible change in the skin's color, appearance, or texture. It can affect a single small area or cover the entire body. When a rash occurs, the skin might become itchy, warm, or bumpy. It can also feel dry, cracked, or blistered. Some people experience swelling or pain alongside these changes. Because so many different things cause rashes, they are very diverse in how they look and feel.

To understand a rash, doctors must perform a careful diagnosis. They look at the specific appearance of the skin lesions. For example, some rashes look like sandpaper, which is typical of scarlet fever. Others appear as plaques with silver scales, a sign of psoriasis. Doctors also examine the distribution, or where the rash is located on the body. Some rashes, like secondary syphilis, appear on the palms and soles of the feet. Others, like chickenpox, tend to follow the hollows of the body.

Symmetry is another important clue during a medical examination. A symmetrical rash looks the same on both sides of the body. In contrast, a condition like herpes zoster usually affects only one side. This helps doctors rule out certain diseases. They also consider the patient's history, such as their occupation or recent travel. A doctor might even order a patch test to identify specific allergens. This test helps determine if a substance caused an allergic reaction.

Many different triggers can cause these skin changes. Allergies to food, dyes, or insect stings often cause hives. You can also react to metals like nickel or zinc. Contact with an irritant, such as poison ivy or balsam of Peru, can cause allergic contact dermatitis. This can result in a red, itchy, or even leathery rash. Other causes include fungal infections like ringworm or skin diseases like acne. Even environmental factors like sun exposure or heat can lead to a rash.

Specific medical conditions produce very distinct types of rashes. Measles causes an erythematous, morbilliform, maculopapular rash. This means it is a red, spotted rash that starts at the head and spreads downward. Lyme disease produces a unique rash called erythema migrans. This circular or oval rash can expand to between 5 and 70 centimeters. It may have a central clearing or a darker center. It can feel warm, though it is usually not itchy or painful.

Other conditions affect specific parts of the body or have unique symptoms. Acne vulgaris often appears on the face, chest, and back. It presents as comedones, papules, or pustules. Pityriasis rosea often begins with one scaly spot before spreading across the chest and abdomen. Some rashes are quite painful, such as shingles or boils. Others, like croup or chickenpox, may come with a fever or sore throat. Even small, firm bumps called warts can form on the skin without itching.

Treatment for a rash depends entirely on its underlying cause. Doctors may recommend topical creams, which are medicines applied directly to the skin. Steroid creams, such as hydrocortisone, are common for many minor rashes. In the United States, many of these treatments are available over the counter. However, these creams have limitations. For instance, hydrocortisone may struggle to penetrate the skin through absorption. This can make it ineffective for anything except very mild cases.