Senile purpura https://en.wikipedia.org/wiki/Solar_purpura
Senile purpura is a skin condition characterized by large, 1‑ to 5‑cm, dark purplish‑red ecchymoses appearing on the dorsa of the forearms and the hands. The purpuric lesions are caused by sun‑induced damage to the connective tissue of the skin. No treatment is necessary. The lesions typically fade within up to three weeks.

Treatment
It is important not to apply steroid ointments.

Mear ynformaasje ― Frysk
References Actinic Purpura 28846319 
NIH
Actinic purpura komt foar as ecchymoses yn de djippe lagen fan de hûd. It komt faker foar by âldere minsken mei connective tissue en blood vessels, benammen as se in soad sun exposure hân hawwe.
Actinic purpura results from the extravasation of blood into the dermis. This phenomenon is due to the skin atrophy and fragility of the blood vessels in elderly individuals, which is exacerbated by chronic sun exposure.