Final answer:
In dermatology, a patch refers to a large, flat, discolored area on the skin, often caused by conditions such as psoriasis or eczema. Patches are one type of skin lesion and are characterized by localized inflammation, which requires careful evaluation to determine the underlying cause.
Step-by-step explanation:
A patch in dermatological terms refers to a flat, discolored area on the skin larger than 1cm in size. Unlike a papule, which is a small raised lesion, patches lie flat on the skin's surface. Patches can have various characteristics and may be caused by a wide range of factors, including localized inflammation of dermis and hypodermis, with skin that may be red, warm, and painful to the touch. Examples of patches include areas of skin affected by psoriasis, which can present as itchy or sore patches of thick, red skin with silvery scales. Patches are also described in the context of other conditions like eczema, which can cause inflamed, swollen areas of skin, often resulting from contact dermatitis or allergic reactions, such as in the case study described where a patient had allergic eczema due to sunscreen.
It's important to understand that patches are one type of skin lesion, which may be indicative of infections, inflammatory reactions, or allergic responses, and can vary widely in appearance. Dermatologists use specific terms to describe these lesions, and careful examination is key in determining the underlying cause which could include infection, allergy, or other skin disorders. The diagnostic process often involves looking at the size, shape, color, and location of the skin abnormality.