Greetings. It's very clear on photo but most likely looks like a pityriasis alba or a mild pmle- a sun allergy. Might have occurred after some sun exposure he's had this summer. You need to see a qualified dermatologist near you and use a very very mild topical steroid cream under prescription for just a week or two. The color of the patch will slowly get back to normal. Warm regards.
Flag this answer
Let others know if this answer was helpful
Was this answer helpful?
Disclaimer : The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.