Alopecia areata presenting as widespread shedding rather than obvious round patches.
Diffuse alopecia areata can resemble telogen effluvium or early pattern hair loss because hair loss is spread across the scalp instead of forming classic coin-shaped patches. Clues may include sudden onset, exclamation mark hairs, yellow dots, black dots, nail pitting or a history of autoimmune disease. It matters because management differs from ordinary stress shedding. Trichoscopy and, occasionally, scalp biopsy can help distinguish it from telogen effluvium, androgenetic alopecia and scarring causes.
BAD alopecia areata: https://www.bad.org.uk/pils/alopecia-areata ; DermNet trichoscopy: https://dermnetnz.org/topics/trichoscopy