What is SPF?
SPF stands for “sun protection factor”. It is a marker of how well a product will protect your skin from the sun. This factor, which can range anywhere from 10 to 50, measures the sunscreen’s ability to protect against UVB rays only. UVB rays are the ultraviolet rays that cause sunburn, skin damage and contribute to skin cancer. The SPF number does not indicate the amount of UVA protection a sunscreen offers. UVA rays are the ultraviolet rays that penetrate deep into the dermis. However, there are broad-spectrum sunscreens that contain ingredients like zinc oxide and titanium dioxide known to block and protect against both UVB and UVA rays.
How SPF works
The SPF is a multiplying factor. It is calculated by comparing the amount of time that it takes to produce the first sign of redness on unprotected skin, versus the time it takes to produce redness on skin that has been protected.
If your skin, when unprotected normally, starts to burn after 10 minutes of sun exposure, a sunscreen with an SPF of 30 would increase that time by a factor of 30, allowing you to stay in the sun 30 times longer than you could without protection. This means you could stay in the sun safely for about 300 minutes. The higher the SPF of the sunscreen, the more UV rays it blocks out.
This is a basic explanation. It’s dependent on lots of factors that affect how well you are protected from the sun. These include your skin type, the amount of sunscreen you’ve used and how active you are. So, relying on the SPF to determine how much time you can spend in the sun is not a good idea.
No sunscreen, regardless of the SPF, should be expected to stay effective for longer than two hours without being reapplied.
Which SPF for your skin?
- Fair complexion: choose a sunscreen with a high SPF. Anything with an SPF of 30 or higher is good.
- Oily or acne-prone skin: go for an oil-free sunscreen.
- Sensitive or allergy-prone skin: opt for a sunscreen containing barrier ingredients such as zinc oxide and titanium dioxide, rather than other chemicals.
- Dry skin: look for chemical and mineral sunscreens that are infused with a hydrating lotion or cream.
Good to know
- When swimming or doing water sports, use a water-resistant sunscreen. Make sure you reapply the sunscreen after swimming and towelling as these activities can reduce the amount of sunscreen on your skin, which can leave parts of your skin vulnerable to harmful UV rays.
- Choose a brand you like. If you don’t like your sunscreen, chances are you won’t use it.
- Pick a broad spectrum sunscreen that protects against both UVA and UVB rays. If in doubt, check for the CANSA seal of recognition on the container.
Safe sunny days
- Avoid the sun between 10am and 4pm when the sun’s rays are most dangerous. If your shadow is shorter than you, the sun’s rays are at its strongest.
- Stay in the shade as much as possible.
- Know the strength of your sunscreen and make sure you use the correct product for your skin type.
- Apply your sunscreen generously. Don’t skimp as this will make the sunscreen less effective. Use at least 30ml (two tablespoons) for your whole body.
- Apply your sunscreen evenly, and make sure you apply it on all exposed skin, including your ears, feet and hands.
- Apply your sunscreen at least 30 minutes before going out in the sun to give it time to bind to your skin.
- Reapply your sunscreen regularly (at least every two hours), especially after sweating, swimming or any kind of physical activity.
- Always combine your source of protection with protective clothing. Wear tightly woven fabrics that are cool, and cannot be seen through when held up to the light. Slap on a hat, preferably one that’s thickly woven, and wide-brimmed. Put on a pair of shades that offer 99-100% UV protection.
If you want to make sure the sunscreen has been tested and approved by the CANSA foundation, look for the CANSA stamp of approval. For a list of products, see here.
If you’re still unsure about what to use for your skin, why not ask one of our doctors? Just log into the app and type your question, and a doctor will get back to you shortly.