According to The Home Remedies Handbook: although few things can penetrate the skin’s outer layer (stratum corneum). The sun’s ultraviolet rays easily pass through this layer and damage the cells and structures beneath. Ultraviolet light comes in two varieties: ultraviolet A (UVA), the so called “tanning rays,” which do not cause sunburn (except at very high doses), and ultraviolet B (UVB), the “burning rays.” UVA rays can pass through window glass while UVB cannot. Both types penetrate the outer layer of the skin and cause damage.
Ultraviolet rays that can pass through the stratum corneum cause pigment-producing cells called melanocytes to produce brown pigment (melanin). This is the skin’s effort to protect itself from the invading rays and prevent further damage to skin structures. How much and how quickly the melanocytes can produce the pigments depends largely on genetics. Dark-skinned people can readily produce melanin, while light-skinned individuals, especially of Northern European ancestry and Orientals, don’t produce it well or produce it in blotches that appear as freckles.
If your skin doesn’t produce the protective melanin pigment well, or if you’re overexposed to the sun before the pigment can be manufactured and dispersed, the ultraviolet rays damage the epidermal cells.
“Even if you develop only a mild redness, you’re killing the top layer of your skin just as you would with a thermal burn from touching something hot.” says James Shaw, M.D., chief of the Division of Dermatology at Good Samaritan Hospital and Medical Center in Portland.
Ultraviolet light can even damage the dermis, the layer of skin that gives your skin its shape, texture, strength, and elasticity. Sunlight breaks down the thick, strong tissue structure of the dermis, rendering it weak, thin, and less elastic and making it appear wrinkled and saggy. . “Once you’ve been overexposed to the sun,” says Shaw, “the damage to the skin is already done,” says Shaw.
So as they say, an ounce of prevention is better than a pound of cure so don’t forget to protect your skin against sunburn.