Noticing an unexpected rash on your skin can be unsettling. A rash may show up as red patches, bumps, blisters, or dry flaky areas, often accompanied by itching, burning, or discomfort. While many rashes are harmless and resolve on their own, some might indicate an underlying health issue that needs attention. Understanding the possible causes of an unexplained rash helps you respond appropriately and take care of your skin.

One of the most common causes of a sudden rash is contact dermatitis. This occurs when your skin reacts to something it has touched—such as soaps, detergents, cosmetics, or plants like poison ivy. The rash usually appears where the irritant touched the skin and may look red, swollen, and itchy. Avoiding the offending substance usually helps the rash heal.

Allergic reactions can also cause rashes. Common triggers include certain foods, medications, insect bites, or environmental allergens like pollen or pet dander. Allergic rashes often appear as raised, red, itchy welts called hives. Sometimes, these reactions can be severe and involve swelling or difficulty breathing, which requires emergency medical care.

Heat rash is another frequent cause, especially during hot and humid weather. When sweat ducts become blocked, sweat gets trapped under the skin, causing small red bumps or blisters. Heat rash is often itchy or prickly and commonly occurs in areas where skin rubs together, like under the arms or around the neck.

Various infections can cause rashes as well. Viral infections such as chickenpox, measles, or shingles create distinctive rash patterns and are often accompanied by fever or fatigue. Fungal infections like ringworm produce circular, scaly patches, while bacterial infections may cause redness, swelling, and pus, often requiring antibiotic treatment.

When dealing with persistent or unexplained skin rashes, UVB phototherapy can be an effective treatment option. It helps reduce inflammation and promote healing, especially in conditions like psoriasis or eczema. Consulting a dermatologist about phototherapy might provide relief when other treatments haven’t worked.