SPF explained | How to makes sense of SPF
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First things first: What does SPF stand for?
How do sunscreens work?
There are several misconceptions about sunscreens. The most prevalent one I encounter as a Dermatologist, however, is how they work.
Chemical sunscreens work by absorbing light. Once the sunscreen maxes out its ability to absorb light, the rest flows over to your skin. Imagine this as a cup on your skin. It’s filling with ultraviolet light (UV). Once the cup fills- the rest of the UV overflows to your skin. Have you ever said ‘I literally wore tons of sunscreen and reapplied and still burned!’ This is why! It is important to note that this is the distinction with physical sunblocks such as zinc or titanium. Physical sunblocks block UV by shielding the skin directly.
The other very important thing to note is the listed SPF on the bottle versus the actual effective SPF when the sunscreen is applied. The actual SPF listed on the bottle is the SPF if the product is applied appropriately- generously. If the sunscreen is applied sparingly and not reapplied when needed, then the effective SPF - the actual effectiveness of the product - can be far less. The SPF starts to wear off because the product wears off.
What are your best tips for shopping for sunscreen?
Look at the ingredients - not the price or name brand. Don’t purchase based on the front of the bottle- look at the back. I ask that my patients really look for Zinc and/or titanium on the active ingredients list. These are physical sunblocks and are more effective at blocking UV.
The challenge with physical sunscreens is that they are not as cosmetically elegant to apply as a chemical sunscreen. Chemical sunscreens do not look as obvious on the skin as they do not tend to leave a whitish cast. Consider reserving the use for chemical sunscreens to the face and hands and either using physical sunscreens and/or sun protective clothing for the rest of the body. This will reduce the body surface area to apply the product which will in turn reduce the exposure and potential absorption of these products.
Which ingredients are most effective in sunscreens and which ingredients tend not to be effective?
See above for the most effective. Anthelios is another effective and good ingredient seen in some brands. The most effective option for over 80 % of the body surface area is sun-protective clothing.
Aside from sunscreen, what are some other ways people can protect themselves from the sun's rays?
Sun protective clothing and accessories are key to sun safety. My research shows that we can effectively protect over 90% of our body surface area with adaptable sun-protective clothing, hats, and sunglasses. I have specifically designed my sun-protective lifestyle brand to address this concern.
When considering clothing and accessories such as hats and sunglasses it’s important to look for the UV blocking properties and not assume that UV is blocked simply because you wear it. The reality is that the actual UV blocking properties of a white T-shirt can be as low as an SPF of 3 and potentially wears down more through washing and drying.
How much SPF should I wear on my face?
A minimum SPF of 30 is reasonable for most people to have adequate protection from excess UV exposure. More important than SPF, however, is understanding the protection your products are offering. SPF only tells us the amount of UVB blocked by your products. UVB is the type of UV associated with sunburns and skin cancer. As we learn more, we are finding that UVA may not be directly linked to skin cancer, but it certainly contributes to deeper long-term damage to our skin that can make it more susceptible to damage by UVB damage as we age. Ideally, I ask my patients to shop for sunscreen based on ingredients - buy a product based on the back of the package and not the front. Look for Titanium and/or Zinc as your active ingredients to have confidence that you are blocking both UVA and UVB while outdoors.
We often hear about the need for a shot glass full of sunscreen to apply to exposed areas of our body, but how much do you need to apply to your face?
The shot glass or one ounce of sunscreen for the body is the amount based on the assumption that the exposed areas will be the areas not covered by a bathing suit.
For the face alone, a nice unit of measurement is the fingertip unit. A fingertip unit, also called an FTU, is a simple measuring tool to help guide how much product to use. One adult FTU is the amount of cream squeezed out onto the fingertip in a line from the first joint skin crease to the tip of the finger. One adult FTU of the product will effectively cover two adult handprints of skin surface area. For most facial products, each hand covers half the face. This would mean a single FTU of cream will cover the face. This is similar to two pea-sized 'globs' of product. Some sources will refer to this amount as about a 1/4 to 1/3 of a tsp. If using a spray-on product, make sure enough is applied to have nice even coverage.
Other measurement guides for facial sunscreen:
- 1/4 to 1/3 tsp
- 1-2 mL
- 1-2 gms
- Nickel size amount
I tend to recommend what I refer to as "dip, dot, then smear" method for applying facial sunscreen. Place the sunscreen in your hand. Dip your finger in, dot it on a cheek, dip again, dot on the other cheek, dip again, dot on your right forehead, repeat for your left forehead, chin and nose. Then smear all over.
The most important note for use of SPF-containing products is the reapplication. Reapplying sunscreen every 2 hours bloodstream regardless of the SPF factor is key to best use practices. This is especially important if sweating or swimming!
How much SPF should my kids wear?
Same as above. One additional note for kids is the news on chemical sunscreens. There have been concerns that chemical sunscreens are absorbed into the bloodstream with unclear long or short-term health impacts. The worry is that some of these ingredients have been thought to be “endocrine disrupters”. Children may be more susceptible to endocrine or hormonal impacts. We favor children to use mineral sunscreens - zinc and /or titanium-containing products - to avoid this issue.
Does SPF clothing work?
Absolutely! Clothing is actually rated for UV protection by its UPF factor. This is different from SPF. UPF is a better rating system as it provides information on the blockage of both UVA and UVB. The best part about sun protective clothing is that it does not wear off the way products can when sweating or swimming. They are ideal and can reduce the amount of sunscreen that needs to be applied. The only caveat is that sun-protective clothing can only protect areas of skin covered by clothing. In other words, a sun-protective bikini is likely not doing a lot to protect the wearer from skin cancer.
What about SPF for lips?
I see so much actinic cheilitis- precancerous changes to the lips (especially lower lip) - I had to find our patients options for this difficult to manage the area. I also have a large number of patients on Accutane and we have to make sure they are sun safe to avoid damaging their lips at a time when their medication makes them even more sensitive to the sun.
It’s a practical issue- sunscreen already wears off, it only wears off faster on a mucosal surface like the lip where food, drink, and lip licking take it off!
Here’s the list we provide our patients- all available on Amazon and online.
EltaMD UV Lip Balm Sunscreen Broad Spectrum SPF 36: Love this because it has my favorite sunblock- zinc- and it’s water resistant.
One of my favorite brands to recommend for people with sensitive skin. This is also gluten free for my patients with gluten sensitivities (big issue if you use a lip product with gluten)
The key features I look for are
- Zinc as the active ingredient
At least SPF 30
Most lip products are in the SPF 15 range. With all the sunscreen absorption safety concerns through our skin, I’m just as worried about sunscreen ingestion through the lips with chemical sunscreen use. I prefer mineral-based sunblocks to recommend for this purpose.
How frequently should I apply SPF?
This depends on if you are sweating or swimming. If you are indoors primarily and only going out temporarily to get to the car or drive home and have not been overly active for your product to wear off, you may not need to reapply. If you are sweating or swimming you may need to reapply every 40 to 80 minutes depending on the water-resistance of the product you choose. Think about how long your lipstick will last if you are not eating or drinking versus through a meal. This is the same concept if you imagine your sunscreen attached to your skin in the same way!
Are SPF products safe?
As I mentioned above- focus on mineral sunscreens as these are generally regarded as safe and effective to use the FDA’s terminology. The other products are still in the process of proving safety data.
Each year the news seems to present more studies that come out evaluating the absorption of chemical sunscreens into our bloodstream after just one day of use.
I discussed these studies with Practical Dermatology and what it means for our patients.
”The most important thing to remember when it comes to sunscreens is that we do have choices. The sunscreens tested in this study were chemical sunscreen. As a Dermatologist and a mother I have always asked my patients to choose sunblock based on the ingredient label and not the brand. Look for active ingredients that you can pronounce- zinc and/or titanium - for most brands.”
”Also remember that sunscreen is only one component of your sun safety plan. Hats, sunglasses and sunsafe clothing will limit your need for the use of sunscreen products.”
What's the best way to care for a sunburn?
After an initial burn, focus on calming down the skin and inflammation associated with it. Taking an NSAID can reduce inflammation. Applying aloe or hydrocortisone creams can help reduce swelling and redness and soothe discomfort.
Take a look at these common over the counter products and how to use them
- Aloe: Aloe Vera is a common go-to sunburn treatment as it is affordable, over the counter, and easy to find. Its effects in managing the impact of sunburn have been studied. Overall, applying aloe to a sunburn can reduce the inflammation and redness associated with the burn. The hope is that by doing so, healing can start to kick in sooner.
- Coconut oil: Coconut oil has some anti-inflammatory effects on the skin but has not been as well studied for treating a sunburn. It is used more commonly and studied for eczema. That being said, its sun protective effects have been minimally studied and found to perhaps block about 20 % of UV rays.
When it comes to managing a sunburn, the first step is focusing on reducing swelling and progression of the burn, soothing the discomfort associated with the burn, and healing in any blisters or eroded areas that develop from skin sloughing after a burn. NSAIDs and anti-inflammatories can help with the first stage and even potentially steroid creams or oral if severe. Soothing discomfort and reducing redness is a great place for aloe to play a role. And, lastly, coconut oil may be better used later in management to help protect and restore the skin as it heals.
I know I can get burned when it's cloudy or sunny; is one worse than the other, or is it the same?
Clouds block about 20 % of UV. A burn is a burn- they are bad for your skin regardless of whether it’s on a sunny or cloudy day. (Once your fry an egg, you can’t un-fry it — this is the most common thing I tell my patients!) in practice, some of the most severe sunburns I have seen have been on cloudy cool days. The reason is simply that the cool temperatures and lack of sunlight give people a false sense of security. They hang out all day and do not feel the sensation of a burn. UV is invisible and temperature is not determined by UV. Temperature is actually dictated by infrared. Assume if you are outdoors, summer/spring/ summer/ fall, midday, you can potentially be at risk for burns and take the appropriate precautions. After all, skiers have a high risk of skin cancer because UV is magnified by fresh snow!