The photo looks most like dry, flaky skin (xerosis) rather than a sharply defined loss of pigment. The whitish appearance seems to be fine surface scaling on the forearm. Dry skin often looks gray-white and rough, especially after bathing, soap use, or dry weather. This cannot be diagnosed with certainty from a photo.

Try:

See a clinician or dermatologist if it becomes very itchy, red, painful, spreads, forms a clearly defined chalk-white patch, develops a ring-shaped border, or does not improve after 2-3 weeks of moisturizing. The AAD dry-skin advice has practical care tips.

From the photo, it looks most like dry, flaky skin (xerosis), which can appear whitish or “ashy,” especially after bathing, soap use, dry weather, or friction. I do not see a clearly defined, smooth white patch that would strongly suggest pigment loss, but a photo cannot confirm a diagnosis.

Try:

See a clinician or dermatologist if it becomes a sharply outlined white area, spreads, is very itchy/red/scaly, painful, or does not improve after 2 to 3 weeks of moisturizing. The medical reference describes dry skin as often gray-white with a rough texture and fine scale.