The correct option is A UV rays
Melanin is produced by cells called melanocytes. The pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, melanin is thought to protect skin cells from UVB radiation damage, reducing the risk of cancer
Melanocyte stimulating hormone secreted by the middle lobe or pars intermedia of pituitary gland, acts on the melanocytes and regulates pigmentation of the skin.