Sunlight, ozone and vitamin D.
D055598:Chemical Phenomena; D002621:Chemistry; D002762:Cholecalciferol / Q000096:biosynthesis* / Q000097:blood; D006801:Humans; D010126:Ozone; D012621:Seasons; D012867:Skin / Q000528:radiation effects; D013472:Sunlight; D014807:Vitamin D / Q000502:physiology
D014807:Vitamin D; D002762:Cholecalciferol; D010126:Ozone