UV Rays

April 10, 2026

This page was reviewed under our medical and editorial policy by Gaurav Singh, M.D., M.P.H., F.A.C.M.S., Mohs Micrographic Surgeon and Dermatologist, City of Hope^® Cancer Center Chicago.

Sunlight is made up of several different types of light. These include the light we see, as well as types of radiation that are invisible to the human eye, such as infrared light and ultraviolet (UV) light. Too much exposure to UV light increases a person’s risk for developing skin cancer because UV rays damage the cells in the skin. Wearing sunscreen, sun-protective clothing and staying in the shade may reduce this risk.

What Is UV Light?

UV light is the name for several wavelengths of light (or radiation) that are emitted by the sun. There are three types of UV rays, named UVA, UVB and UVC.

UVA Rays

Too much exposure to UVA rays has been linked to higher rates of skin damage and skin aging. It may also contribute to a higher risk of skin cancer. This is in part because the Earth’s atmosphere cannot absorb UVA rays very well, so this type of radiation reaches the planet’s surface easily. Most UV light that reaches humans is UVA light.

UVB Rays

UVB rays may cause skin cancer, skin aging, sunburn and snow blindness. It is the type of UV light that is most directly linked to a greater risk for developing skin cancer. Although the atmosphere absorbs most UVB light, some UVB rays still make it to the Earth’s surface.

UVC Rays

UVC rays are almost completely absorbed by the Earth’s atmosphere and have a negligible effect on skin cancer risk.

UV Radiation and Sun Damaged Skin

Being exposed to UV light may cause damage to the DNA that tells skin cells how to function. If too much cell damage accumulates over time, this may lead these cells to behave abnormally, growing out of control and forming a tumor. These tumors may be benign, or noncancerous, at first, however, they may become cancerous over time.

What Is the UV Index?

The UV index is a way to measure how strong UV radiation from the sun may be on any given day. A UV index forecast is often included alongside a standard weather forecast.

The UV index rates the likely strength of the sun’s UV rays using a number usually between 1 and 9, although the scale may sometimes run higher than that. In general, if the UV index is 3 or above, this means that UV rays are at a moderate to high level and that sun protection should be used when outdoors.

What UV Is Good for Tanning?

There is no healthy amount of UV light for the skin and exposure to any UV light has been linked to both skin damage and skin cancer. This means that the only safe way to tan is to use sunless tanning products, such as tanning sprays or creams. It is also important to know that a tan does not protect the skin from UV light.

Preventing Damage From UV Rays

There are some easy ways people can protect themselves from the damage that UV light causes to the skin. These include:

• Wearing broad-spectrum sunscreen with an SPF of at least 30 whenever out in the sun
• Reapplying sunscreen every two hours, or more frequently if swimming or sweating a lot
• Avoiding being outside in the sunlight between around 10 a.m. and 4 p.m., when the sun’s UV rays are at their strongest
• Seeking out shade when it is hot and sunny outside or using an umbrella to create shade
• Wearing a broad-brimmed hat and sunglasses to protect the face and eyes from the sun
• Using sun-protective clothing with long sleeves