From the Guidelines
You should wear sunscreen on cloudy days to protect your skin from harmful ultraviolet radiation. Clouds only block about 20-40% of UV rays, meaning 60-80% of harmful ultraviolet radiation still reaches your skin even when it's overcast [ 1 ]. UVA rays, which cause premature aging and contribute to skin cancer risk, can penetrate clouds and even glass. For adequate protection, apply a broad-spectrum sunscreen with at least SPF 30 about 15 minutes before going outside, using approximately one ounce (enough to fill a shot glass) to cover exposed areas of the body. Some key points to consider when using sunscreen include:
- Reapply every two hours, or more frequently if swimming or sweating
- Use sunscreen in combination with other protective measures, such as wearing tightly woven protective clothing and seeking shade whenever possible [ 1 ]
- Daily use of sunscreen with a high sun protection factor (>15) on exposed skin is recommended for residents of areas of high insolation who work outdoors or enjoy regular outdoor recreation [ 1 ] This practice helps prevent sunburn, reduces skin cancer risk, and minimizes premature aging effects like wrinkles and dark spots. Many people mistakenly believe they're safe from sun damage on cloudy days, but maintaining consistent sunscreen use year-round regardless of weather conditions is essential for long-term skin health [ 1 ].
From the Research
Importance of Sunscreen on Cloudy Days
- The question of whether to wear sunscreen on cloudy days can be informed by understanding how sunscreens work and the potential risks of UV radiation [(2,3)].
- UV radiation from the sun can cause skin damage, photoaging, and skin cancer, regardless of cloud cover 3.
- Sunscreens can provide protection against UVA and UVB radiation, with different ingredients offering varying levels of protection [(2,4)].
Mechanism of Sunscreen Protection
- Sunscreen ingredients like zinc oxide and titanium dioxide provide protection primarily through absorption of UV radiation, rather than reflection or scattering 5.
- The use of these ingredients in sunscreens can help prevent skin damage and skin cancer 6.
- Avobenzone is another ingredient that provides broad-spectrum protection, but its effectiveness can depend on the formulation and stability of the sunscreen product 4.
Cloud Cover and UV Radiation
- While cloud cover can reduce the intensity of UV radiation, it does not eliminate the risk of skin damage and skin cancer 3.
- UV radiation can still pass through clouds, especially during peak sun hours, making sunscreen use important even on cloudy days 3.
- The UV index can be used to determine the level of sun protection needed, regardless of cloud cover 3.