SPF Sunscreen limitations & Application Tips
Sunscreen limitations and changes with application density
Sunscreen is one of the primary methods we can use to help protect our skin from UV radiation. It prevents the development of photodamage, photoaging, and the consequences of excessive sun exposure: skin cancer.
What is SPF?
SPF is also known as sun protection factor. It is a relative measure of a sunscreen’s ability to protect and prevent UVB radiation from damaging the skin. UVB rays damage the outermost layer of the skin known as the epidermis. By causing damage to the most superficial skin layers, UVB rays can cause reddening of the skin, sunburns, and the most common forms of skin cancers such as basal cell carcinoma, and squamous cell carcinoma.
It is important to note that SPF is not a measurement for UVA radiation. UVA radiation differs from UVB in that it causes damage to the deeper layers of the skin, known as the dermis, and is associated with aging. However, like UVB rays, UVA has the potential to cause skin cancers.
The Amount of Sunscreen Counts
Studies have shown that even though the SPF labeled on the sunscreen may correctly indicate the sunscreen’s ability to shield UVB radiation, many users are not achieving that SPF level. This is because the majority of consumers are not applying enough and are only applying on average a quarter of the recommended amount to achieve adequate UV protection. The SPF value labeled on the sunscreen is based on the use of a sunscreen layer of 2mg/cm2, however most users only apply about a sunscreen layer of 0.5mg/cm2. Therefore the SPF value is significantly lower than expected.
How to know the right amount for adequate protection
To help visualize how much sunscreen an individual needs, it is estimated that the surface area of the face requires roughly ¼ teaspoon-worth of sunscreen. However, for many individuals, this may seem too much to apply all at once. Therefore, it is now commonly recommended to do a double application of sunscreen. After allowing the skin to dry after the first application of about 1mg/cm2, users are encouraged to reapply sunscreen of about 1mg/cm2.
Double application helps consumers to reach an adequate amount of sunscreen needed to achieve the expected SPF efficacy and sun protection.
Is a Higher SPF Truly Better?
SPF values are not rated on a linear scale. A sunscreen with an SPF of 30 does not provide double the protection of a suncreen with an SPF of 15. An SPF 15 sunscreen blocks about 94% of UVB rays and an SPF 30 sunscreen blocks 97% of UVB rays. No matter how high the SPF value, no sunscreen can provice 100% protection.
Furthermore, because it is assumed that most users are using an inadequate amount of sunscreen, it has been shown that applying higher SPF sunscreens may provide more adequate protection and clinical benefits than lower SPF sunscreens. By using a sunscreen with a higher SPF, the user may achieve an actual SPF that meets the minimum SPF level recommended for photodamage and skin cancer prevention. It is important to note that despite using high SPF sunscreen, reapplication is essential and limiting sun exposure is still important. The general rule of thumb is to reapply sunscreen every 2 hours, or more frequently if needed when swimming, sweating, or performing prolonged activities outdoors. Many individuals who use a sunscreen with a higher SPF may have a false sense of safety and believe they can stay in the sun for a longer period of time. This can lead to overexposing themselves to UV radiation resulting in increased risk for radiation sequelae, particularly skin cancer.
It is generally recommended that individuals use a sunscreen with an SPF of 30 to 50.
Does high SPF sunscreen reduce vitamin D production?
A common controversial topic is the effects of sunscreen use on UV dependent synthesis of vitamin D3 on our skin. Vitamin D3 synthesis requires exposure of UVB rays and because sunscreen blocks UVB rays, it is believed that regular sunscreen application may cause vitamin D insufficiency. However, even when sunscreen is applied appropriately some UVB radiation still penetrates the skin and only a limited amount of sun exposure is necessary for vitamin D3 synthesis on our skin. However, regular sunscreen use may increase the likelihood of developing vitamin D insufficiency if individuals have other health conditions that may decrease their ability to absorb vitamin D. For the general population, however, regular sunscreen use alone does not cause vitamin D insufficiency.
Tips for Using Sunscreens
- Use a sunscreen with broad-spectrum UVB and UVA coverage
- Use sunscreen on a daily basis: even when indoors for most of the day or on a cloudy rainy day
- At the minimum, use a sunscreen with an SPF of 30
- Apply liberally (about 1/4 teaspoon for the surface area of the face) and uniformly, or use the double application method where the sunscreen is applied twice in a row
- Reapply after 2 hours if not sooner when engaging in outdoor activities where sweat and water can decrease the efficacy
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- Teramura T, Mizuno M, Asano H, et al. Relationship between sun-protection factor and application thickness in high-performance sunscreen: double application of sunscreen is recommended. Clin Exp Dermatol.2012;37(8):904-908; PMID: 23050556 Link to research.
- Sunscreens Explained. Skin Cancer Foundation. 2012.
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