Sunscreen and UV filter myth busters – SPF

Welcome to the third blog from the sunscreen and UV filter myth busters series. There are so many myths surrounding sunscreens and SPF, it can be hard to separate fact from fiction. And while the majority of myths are spread by social media, we are also seeing some common misconceptions spread within our industry.

I have gathered together the other solar experts here at Croda to debunk some of the biggest sunscreen and UV filters myths. In this blog we are tackling some misconceptions that the general public have about sunscreens and SPF.

Mythbusting with Croda

Myth 1: Will a base tan protect me from the sun?

There is no safe or healthy way to get a tan, unless you use fake tan. Tanning is a response to exposure to UVA, which penetrates the dermis and stimulates the production of melanin. A tan does not protect your skin from the sun’s harmful effects in the same way as a sunscreen, in fact experts estimate that going out in the sun with a base tan is equivalent to wearing an SPF 3 or less sunscreen.1

Also, as it is UVA that causing ageing, then the more you tan, the more you’ll wrinkle. Furthermore, exposure to UV rays is the leading cause of skin cancers. Experts are in consensus on this topic, the risks and drawbacks of long-term tanning far outweigh the minimal benefit of a base tan.

woman reading a book in the sunshine

Myth 2:  If my sunscreen is SPF 50 can I apply it less often?

This is false. The SPF number refers to how much protection you are getting from the sunscreen, but not how long it lasts.  No matter the number associated with the SPF, sunscreen only works for as long as it stays in an even film on the skin. That is why experts recommend reapplying regulatory and after activities like swimming and sports.

So what does the SPF number actually mean?

SPF testing of sunscreens is carried out on human volunteers where the test sunscreen is applied in small area on the back at 2 mg per cm2. This quantity is roughly equivalent to around ¼ teaspoon for the face, or a shot glass full for the body. A UV lamp is used to test unprotected, and sunscreen protected skin, and the times required for redness (erythema) to appear are recorded. The following calculation is used to give the SPF:

SPF = MED* (protected with sunscreen) / MED (unprotected without sunscreen)

*MED stands for minimum erythemal dose

As an example, if a person normally gets burned in 10 minutes under the lamp, a sunscreen that stops them from burning for 150 minutes (15 times longer) would be classified as SPF 15:

SPF = 150 min (protected) / 10 min (unprotected) = 15

So, the SPF means how much longer it takes your skin to burn with sunscreen on, compared to no sunscreen at all. However, it is important to remember that this is a measurement in a controlled environment and in real life condition UV levels can vary throughout the day. So, experts recommend using a sunscreen that is SPF 30 or higher and reapplying it every two hours. Also, it is important to remember UVA protection. This is not considered in the SPF calculation, so look for the UVA rating on pack.

For formulators looking to achieve a particular SPF or UVA protection level then Croda has developed the Solaveil Calculator which enables you to select products from our mineral sunscreen range and see what SPF and UVA you could achieve at various use levels. To try our Solaveil Calculator, click here.

Myth 3: Does using sunscreen lead to vitamin D deficiency?

Everyone needs Vitamin D, it is essential for healthy bones, it can help boost the immune system, and recent research suggests it may play a role in preventing several diseases. Vitamin D production in skin is triggered by UVB light.

It is a commonly held belief that using a sunscreen and other forms of UV protection leads to vitamin D deficiency, and therefore the best way to obtain enough vitamin D is through unprotected sun exposure. However, this is not true.

“Studies have never found that everyday sunscreen use leads to vitamin D insufficiency,” an article published by the Skin Cancer Foundation states. Even if you thoroughly apply sunscreen, it still allows 2 to 3 percent of the sun’s UVB to reach your skin, and your body only needs a little to produce vitamin D.

Furthermore, you can get vitamin D from foods and supplements, and if you are found to be deficient in this essential nutrient then experts agree this is the safer way to go.

Myth 4: Can I mix bronzer or tints into my sunscreen?

The truth is that mixing anything into a sunscreen can destabilise the sunscreen formulation. Aline Souza Croda’s sunscreen formulation expert explains “The key to achieving good SPF protection comes from achieving a homogenous sunscreen film on the skin. As a formulator we carefully optimise the formula (usually an emulsion) ensuring the UV filters are stabilised within the system, so that when it is applied to the skin it gives the best possible SPF. Mixing another formulation into an already optimised sunscreen formulation is highly likely to destabilise it and therefore negatively impact the SPF.”

The recommended approach here is to layer your products, ensuring your sunscreen film has had time to dry and settle on the skin before putting anything else on top.

applying makeup in the mirror

Myth 5: Is foundation with SPF enough UV protection?

This is another common make-up myth. While experts agree that SPF in make-up products is a great step forward, it is not necessarily sufficient to protect your skin. It all comes down to the amount you use. If you were to use 1/4 tsp for your face then you will get the SPF protected stated on the pack, but that is a lot of foundation. In reality, most people would use a lot less foundation than that. A more practical approach is to apply a layer of sunscreen to the face before applying your foundation. If your foundation also has SPF this is a great way to get even better skin coverage of UV filters.

Myth 6: Do chemical sunscreens need 20 minutes to activate?

All UV filters provide UV protection as soon as they are applied, irrespective of whether that are chemical (organic) or mineral (physical) UV filters. However, for a formulation to provide the best possible protection it must form an even and coherent film on the skin. This process of dry down and binding to the skin takes time. The dry down process is important as sunscreens are mainly emulsion systems that undergo a process call de-emulsification. Once this has occurred and the sunscreen film has dried it is much more likely to stay on the skin and not rub off. When SPF testing is conducted the sunscreen is left for 15 minutes to dry down before the measurement is taken. It is for this reason that you will see the application advice on pack referring to applying sunscreen for 15-20 minutes before UV exposure.

Myth 7: Do I need to wear sunscreen indoors?

While UVB rays are blocked by glass, UVA rays, which cause premature skin aging, skin pigmentation and may increase your risk of skin cancer, are not. The Skin Cancer Foundation recommends wearing sunscreen if you are close to a window for a prolonged period of time, for example if you on a long car commute or if your desk is next to a window.2

woman typing on laptop

So, that concludes our myth busting blog on some of the common myths about sunscreens and SPF. If you found it interesting, why not check out or other myth busting blogs? In part 1 we tackled some of the main myths around “nano” and particle science, click here to read. In part 2 we addressed the topic of “clean” sunscreens, “coral safe” and environmental impact, click here to read.

Sharing science-based facts and educating consumers about the importance of UV protection is core to what we do at Croda, and together we can support you in developing safe and effective sunscreens that help consumers maintain skin health and protect them from skin cancer and photo-aging.

If you would like any more information on the topics discussed in this blog, or support in your sun care developments, don’t hesitate to contact us where our sales representative can put you in touch with one of our formulation experts in your area.



Published by

Helene HineGlobal Marketing Manager