WHAT DOES THE SPF NUMBER INDICATE AND WHICH SUNSCREENS SHOULD YOU CHOOSE?

Dr. Riccardo Matera, Research and Development

Our characteristic skin tone depends on the amount and type of melanin present in our skin, which contributes to defining our phototype — that is, our individual sensitivity to sun exposure.

It has now become common practice to choose sunscreens with a sun protection factor (SPF) appropriate for our phototype to ensure optimal sun protection. The sun’s beneficial effects on mood are well known, as is its role in stimulating vitamin D production, an essential factor for bone health and the immune system.

Do sunscreens prevent vitamin D production?

The conversion of vitamin D in the skin from its inactive to active form is a reaction that takes significantly less time than tanning. This means even short periods of sun exposure are beneficial for the body. Sometimes, unreliable sources claim that sunscreens block these benefits, but it is now well established that people who regularly use sunscreens are often the same individuals who enjoy spending more time in the sun. As a result, they tend to maintain high levels of vitamin D. In fact, recent studies have confirmed that regular use of sunscreens does not cause vitamin D deficiency.

While we are in the sun, we should apply sunscreen suitable for our phototype, making sure to use a higher SPF at the beginning of the summer season. Sunscreen should be applied 20 minutes before sun exposure and reapplied every 2 to 3 hours, especially after swimming or excessive sweating. It is known that the intensity of solar radiation depends on various factors such as latitude, altitude, time of day, cloud cover, and the reflective power of the surroundings. Generally, very fair skin requires high SPF products, usually 30 or 50+.

But what does the SPF number actually mean?

The SPF number indicates the amount of UVB radiation that potentially reaches the skin if the sunscreen is applied as directed. For example:

• SPF 30 allows about 1/30 (3.3%) of UVB rays to reach the skin, filtering 96.7%

• SPF 50 filters approximately 98%, allowing 1/50 (2%) of UVB rays through

Both SPF 30 and SPF 50 provide excellent protection if applied correctly. Sunscreens should be stored away from heat and used in generous amounts. Generally, an adult needs about:

• 5 grams (1 teaspoon) for the face and décolleté

• One teaspoon for each arm or leg

• One for the front and one for the back of the torso
  This totals to approximately 35 mL of sunscreen per full-body application.

Which sunscreens should you choose?

A broad-spectrum sunscreen protects against both UVA and UVB radiation.

• UVA rays penetrate deep into the skin, interacting with dermal cells and causing long-term effects such as wrinkles, loss of tone and elasticity, photo-aging, discoloration, hyperpigmentation, and contributing to skin cancer.

• UVB rays affect the superficial layers of the skin (epidermis), and are mainly responsible for tanning, but also sunburn, erythema, and allergic reactions.

It is therefore essential to protect the skin from both UVA and UVB rays. An important safety feature is the photostability of the sunscreen filters — some filters, once exposed to sunlight, degrade quickly and no longer serve their protective purpose.

After taking all common-sense precautions — like protecting your head, wearing covering clothing, and regularly using sunglasses — don’t forget your sunscreen, your last line of defense against sunburn and erythema.

Kawada A. Risk and preventive factors for skin phototype. J Dermatol Sci. 2000;23 Suppl 1:S27‐S29. doi:10.1016/s0923-1811(99)00074-2

 Passeron T, Bouillon R, Callender V, et al. Sunscreen photoprotection and vitamin D status. Br J Dermatol. 2019;181(5):916‐931. doi:10.1111/bjd.17992