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Why should I wear sunscreen on a cloudy day?

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The question

I've been told to wear sunscreen, even in the winter, and even when it's not sunny. Is this actually necessary?

The answer

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While this may seem unnecessary, you must protect yourself with sunscreen even when it's not sunny as the ultraviolet (UV) rays can still reach your skin and cause potentially harmful damage.

UV rays are known to cause sun burns and age related changes in the skin, but can also cause damage to the skin that can potentially lead to skin cancer.

UVA and UVB rays pass through clouds and glass, so even on overcast days (or if you are working inside near a window) the rays can penetrate and cause damage to your skin. In winter, UV rays still occur and can reflect off snow so protection is necessary throughout the year.

If the sun is up and you're spending prolonged periods of time outside - keep your skin safe and wear sunscreen.

Here are some other quick tips to protect yourself on any day, for any season, sunny or not:

1. Be savvy with your sunscreen use: Choose sunscreens that offer protection to both UVA and UVB rays (broad-spectrum sunscreen) and has a SPF (Sun Protective Factor) of 15 or more. If you're spending prolonged periods of time outside, swimming or sweating - reapply regularly. Remember to check your sunscreen's expiration dates too as they can lose their effectiveness over time.

2. Avoid the strongest sun ray times: In general in North America, the strongest sun rays are between 10 a.m. - 4 p.m., so if possible, limit time outdoors during this time.

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3. Spend time in the shade: While shade does not offer full protection because of the reflection of UV rays off concrete, sand and snow - it can help to minimize direct damage from rays.

4. Cover up with clothing: Long sleeved shirts and pants can be helpful and hats with wide brims can protect the face, ears and neck from UV rays.

Send family doctor Sheila Wijayasinghe your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

Read more Q&As from Dr. Wijayasinghe.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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