发痒 (fā yǎng) is a verb meaning 'to become itchy' — describing the onset of an itching sensation, often sudden or gradual, on the skin. The character 发 (fā) here functions as a verb meaning 'to emit', 'to arise', or 'to begin to show', while 痒 (yǎng) means 'itchiness' or 'an itching sensation'. Together, they form a compound verb indicating the emergence of that sensation — not the state of being itchy (which would be 瘙痒 or simply 痒), but the *process* or *moment* when itchiness starts.

This word is commonly used in health-related contexts: insect bites, allergic reactions, dry skin, or mild skin irritations. It’s neutral in register and appears frequently in spoken Mandarin and medical advice. Unlike adjectives like 痒的 (yǎng de), which describe a static condition, 发痒 emphasizes change and development — similar to English verbs like 'break out', 'start to itch', or 'become itchy'.