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There are several possibilities - More details are necessary to have an idea.
If they are coming and going - it may an allergic rash
If they are persisting - it may be a fungus infection of the skin.
If they are limited to exposed parts only - it may be light sensitivity / so on
A skin specialist (Dermatologist
) is the appropriate doctor.
In case of doubt, they may do blood tests, scrapings for lab tests and so on...
Wishing speedy recovery