After a peeling
sunburnSunburn
Sunburn first aid, the skin often reddens after sun, even with protection. This is because the non-burning rays still get through. The redness does not mean he is getting more damage. There is no treatment for the redness. (A girl would use makeup.) As long as your son uses #30 sunblock--which he should do anyway--he should be fine. One sunburn doesn't cause meaningful permanent damage.
Best.
Dr. Rockoff