Does sunscreen cause vitamin D deficiency?
In everyday real-world use, sunscreen does not cause vitamin D deficiency. Studies show that most people do not apply sunscreen in amounts thick enough, or cover enough body surface area, to meaningfully block vitamin D synthesis. Brief daily sun exposure on arms and legs, even with sunscreen on the face, is generally sufficient.
Vitamin D is primarily synthesised through UVB exposure on the skin. Most people only apply sunscreen to the face and leave arms and legs exposed, which allows adequate synthesis. A review published in the British Journal of Dermatology found no evidence that normal sunscreen use leads to vitamin D deficiency in the general population. If you are concerned about your vitamin D levels, a blood test is the most reliable way to check.
Sources:
British Journal of Dermatology, Passeron et al., 2019. Sunscreen photoprotection and vitamin D status.