If it's not sunburn it could be seborrheic dermatitis
"
Seborrheic (seb-o-REE-ik) dermatitis is a common skin condition that mainly affects your scalp. It causes scaly patches, inflamed skin and stubborn dandruff. It usually affects oily areas of the body, such as the face, sides of the nose, eyebrows, ears, eyelids and chest"
You can get Dermovate from a Chemist(cost < 300 baht) e.g. Boots without prescription - I believe it requires a prescription in the UK