It looks like Photo (light) induced reaction.
This mostly occurs on the exposed parts and in people who indulge in outdoor activities in mid - afternoon times.
Next Steps
•Restrict outdoor activities between 11am and 3pm.
•Liberal use of broad spectrum sunscreens 30 min before going out. This has to be repeated every 3 hrs if required in the daytime.
•Physical protection like umbrella, wide -brimmed hat is preferable.
Health Tips
With these above measures, if it doesn't subside within 6 weeks; also if you have previous history of any other allergies, better to consult a dermatologist.