Sunlight is one thing that can cause mutations. How does sunlight affect our DNA? Sunlight creates structures called thymine dimers, which means that two thymine (T) bases (T) on the same DNA strand become connected in an abnormal way, instead of correctly attaching to the complementary base adenine (A) on the opposite strand. Thymine dimers create kinks in the DNA shape. These kinks make DNA difficult to copy, which can cause a mutation. In order to avoid thymine dimers from developing in our cells, it is very important to use sunscreen to help block ultraviolet A and B (UVA and UVB) rays. The United States Food and Drug Agency (FDA) recommends a sun protection factor (SPF) of at least 15, to protect against skin cancer and early skin aging. Sunscreen should be reapplied every 2 h or after swimming, sweating, bathing, or using a towel. Some individuals who have especially sensitive or light skin should consider higher levels of UV protection and are encouraged to consult a doctor called a dermatologist, who is an expert on keeping skin healthy.

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