Glow is caused by several factors. The most important is the eveness of the skin's outer layer (stratum corneum). The more even it is, the more the skin reflects light.

Other factors are the quality and number of the blood vessels nourishing the skin, the health of the second layer (epidermis) which gets damaged by UVA and B, and the thickness and health of the collagen (deeper in the dermis).

Next week - how to get your glow back.