Rash is a broad term for any noticeable change in the skin’s appearance, texture, or color, often involving redness, bumps, blisters, scales, patches, or itching—ranging from mild and temporary to serious indicators of underlying issues. Common causes include allergic reactions (e.g., contact dermatitis from irritants like poison ivy, soaps, or jewelry, causing red, itchy, blistering patches where contact occurred), eczema (atopic dermatitis: dry, inflamed, intensely itchy areas often in skin folds), psoriasis (thick, silvery-scaled plaques on elbows/knees/scalp), hives (urticaria: raised, itchy welts that come and go quickly, often from allergies or stress), heat rash (prickly heat: small red bumps from blocked sweat ducts), infections (bacterial like impetigo, viral like chickenpox/measles/shingles with clustered blisters or widespread spots, fungal like ringworm), autoimmune conditions (e.g., the classic butterfly/malar rash across cheeks and nose in lupus), drug reactions, insect bites, or even systemic illnesses (e.g., viral exanthems in kids). Symptoms can include itching, burning, pain, swelling, oozing, crusting, or fever if infectious/systemic. Most rashes are benign and improve with home care (cool compresses, moisturizers, OTC hydrocortisone or antihistamines, avoiding triggers), but see a doctor promptly if the rash spreads rapidly, involves the face/eyes/genitals, is accompanied by fever, swelling, difficulty breathing, severe pain, blistering/peeling, doesn’t improve in a few days, or if you’re unsure of the cause—dermatologists often diagnose via exam, history, or tests, and treatment may involve prescription creams, oral meds, or addressing root causes.