At first, it may have looked like an ordinary skin irritation. A small red spot appeared near the back of an older man's neck, just below his hairline. Perhaps he assumed it was caused by sweat, a new shirt, an insect bite, or the products he used to wash his hair. Like many people, he may have believed that a minor skin problem would eventually disappear on its own.
But then something changed.
More spots appeared. Some became red and inflamed, while others developed dark crusts or scabs. The affected skin looked irritated, uneven, and uncomfortable. The rash seemed to spread from the area behind his ear toward his neck and upper shoulder.
Looking at an image like this, many people immediately wonder the same thing: What could cause skin to become so severely irritated, and when should a person stop treating a rash as a minor inconvenience?
The answer is not always straightforward. Skin conditions can look remarkably similar even when their causes are completely different. An infection, an inflammatory disorder, a reaction to a medication, or another medical problem can sometimes produce redness, bumps, blisters, or crusted lesions
