It might be a common skin condition called pityriasis alba. This isn't something to worry about. Pityriasis alba can lead to pale patches on the skin, mainly on the face, neck, and arms. You can see them better in summer when your skin is darker. Dryness is what makes the skin turn lighter than it’s supposed to be, the reason for this happening is mostly because of dryness. You might also want to consider moisturizing your skin more often with lotion, or drinking plenty of water helps too. If there is no change after doing all these things then go to a dermatologist who will advise on treatment methods for this condition.