Your body’s biggest organ, your skin shields you from the elements—but while it’s tough, it’s not impenetrable. Allergens, environmental irritants, infection, hereditary factors, and stress are just a few of the forces that can trigger or exacerbate skin troubles. The terms “skin condition” and “skin disorder” are used interchangeably to describe various skin problems, from small red bumps on the skin to widespread rashes. Some skin conditions can be unsightly but harmless, while others may be contagious. Many skin conditions are also itchy or painful. Allergic skin conditions occur when allergens (certain foods, animal dander, wool, or soaps, for example) trigger an immune system response, such as redness and itching. Viruses, fungi, bacteria, or parasites can also cause skin issues to develop. Some skin problems have a genetic component. For example, eczema, which causes weeping, blister-like rashes, is more common in allergy-prone families. To diagnose skin conditions, doctors typically consider a person’s medical history and physical symptoms. Assessing the size, shape, location, and color of bumps, blisters, and rashes can help doctors pinpoint the exact cause. Other non-skin symptoms may offer clues as well. Sometimes doctors must remove a growth or take a skin sample for examination under a microscope.