Sunscreen Guide - SPF, Application, Kids & Vitamin D

Pradeep Khatiwada^a, Anupam Raj Nepal^a

^a B. P. Koirala Institute of Health Sciences, Dharan, Nepal

Figure 1.

Background

Sunscreen is essential for protecting your skin every day, but if you’re using it the wrong way, you may still be vulnerable to harmful UV rays. Sunscreen reduces your risk of skin cancers and precancers, and helps prevent early aging like wrinkles, sagging, and dark spots. Choosing the right Sun Protection Factor (SPF) and applying it correctly is key to keeping your skin protected and healthy.

What Does SPF Mean?

SPF stands for Sun Protection Factor. SPF tells you how long sunscreen can protect your skin from getting red or sunburned. For example, if you wear SPF 30 the right way, it means you can stay in the sun 30 times longer without a sunburn than if you weren’t wearing any sunscreen.

Is Your Technique Reducing Protection?

Rubbing sunscreen too hard can reduce its effectiveness. Studies suggest that excessive rubbing may decrease its protective power by up to 25% and increase the risk of sunburn. [1] Instead, gently smooth sunscreen over your skin, apply enough sunscreen, and reapply every two hours.

SPF 30 or 100+? What Do You Need to Choose?

While SPF 30 is the minimum recommended for daily use, higher SPFs can offer more protection, especially in real-world settings where coverage and reapplication are often imperfect. When you choose SPF 100+, it can significantly outperform SPF 50+ in protecting the skin. [2] So, when spending long hours outdoors, whether on a hike in the hills or skiing in the mountains, it's better to choose sunscreens with higher SPF.

Best Practices for Application

Many people apply too little sunscreen, miss key areas, or forget to reapply. Proper application is a game-changer.

A general rule of thumb

• Use a nickel-sized amount for the face and a shot-glass amount for the body.
• Apply to all exposed skin. Make sure to apply sunscreen to every part of your body that’s exposed to the sun, including spots people often forget, like the tops of your ears, the back of your neck, your scalp where your hair parts, the tops of your feet, and behind your knees.
• Reapply every two hours or more often if you're swimming or sweating. [3]

Common Side Effects and How to Avoid Them

Sunscreen includes active ingredients that help prevent the sun’s UV rays from reaching your skin. Some individuals experience breakouts, irritation, or allergic reactions to certain sunscreen ingredients such as fragrances or chemical filters. Mineral sunscreens with zinc oxide or titanium dioxide reflect and scatter the rays (like a shield) before they penetrate your skin. They are often better for sensitive skin. [4] Read the label and choose what suits your skin.

Does Sunscreen Block Vitamin D?

It’s a myth that sunscreen causes vitamin D deficiency. Although sunscreen blocks UVB rays which are responsible for vitamin D synthesis, most people don't apply it thickly or often enough to cause a deficiency. You can also get vitamin D from diet and supplements. [5] Skipping sunscreen to get vitamin D is not worth the skin damage.

Sunscreen for Kids: What to Know?

Sunscreen is not recommended for babies under 6 months; instead, keep them in the shade and dress them in protective clothing. For children older than 6 months, mineral sunscreens with zinc oxide or titanium dioxide are ideal. Apply 15 minutes before going outside and reapply every two hours, especially after water exposure. [6]

Are There Alternatives to Sunscreen?

Nothing replaces sunscreen and its protection. However, there are additional sun protection methods like wide-brimmed hats, UV-protective sunglasses, and UPF clothing that can enhance safety. Strategies like staying in the shade and avoiding sun exposure between 10 a.m. and 4 p.m. when the UV index is high can help. [7]

Conflict of Interest

The authors have no conflict of interest to declare.

References

1. Heurung, A. R., Rundle, C. W., & Dunnick, C. A. (2023). The effect of application technique on sunscreen efficacy. *Photodermatology, Photoimmunology & Photomedicine, 39*(1), 12–18. https://doi.org/10.1111/phpp.12801
2. Williams, J. D., Maitra, P., Atillasoy, E., Wu, M.-M., Farberg, A. S., & Rigel, D. S. (2018). SPF 100+ sunscreen is more protective against sunburn than SPF 50+ in actual use: Results of a randomized, double-blind, split-face, natural sunlight exposure clinical trial. Journal of the American Academy of Dermatology, 78(5), 902–910.e2. https://doi.org/10.1016/j.jaad.2017.12.062
3. Kobwanthanakun, W., Silpa-archa, N., Wongpraparut, C., Pruksaekanan, C., & Manuskiatti, W. (2021). An evaluation of the course of facial sunscreen coverage and sustainability over an 8‐hour workday among outdoor workers. Health Science Reports, 4(3), e350. https://doi.org/10.1002/hsr2.350
4. Ou-Yang, H., Stephens, T. J., & Appa, Y. (2012, April). Design and testing of a physical sunscreen for use on sensitive skin. Journal of the American Academy of Dermatology, 66(4, Suppl. 1), AB175. https://www.jaad.org/article/S0190-9622(11)01964-5/abstract
5. Neale, R. E., Khan, S., Lucas, R. M., & Waterhouse, M. (2019). The effect of sunscreen on vitamin D: A review. *British Journal of Dermatology, 181*(5), 907–915. https://doi.org/10.1111/bjd.17992
6. CDC. (2024). Sun exposure. In *Yellow Book: Health Information for International Travel*. Centers for Disease Control and Prevention. https://wwwnc.cdc.gov/travel/yellowbook/2024/environmental-hazards-risks/sun-exposure
7. Lund, J., Tan, E., & Sheehan, J. M. (2024). Evaluating sun protective clothing as a supplemental strategy to sunscreen use. *Photodermatology, Photoimmunology & Photomedicine, 40*(2), 88–95. https://doi.org/10.1111/phpp.12888