Sunscreen

Use broad-spectrum (UVA + UVB) sunscreen, sun protection factor (SPF) 30–50, or 50+ if you have very fair skin or a melanoma history, whenever you'll be outdoors past a brief vitamin D window: long beach days, hiking, outdoor work. If you wear high-SPF sunscreen every day, keep oral vitamin D topped up in winter.

The trial behind it

The evidence comes from Nambour, a town in Queensland, Australia. There, 1,621 adults were randomly assigned either to apply SPF 15+ sunscreen to the head, neck, arms and hands every day for 4.5 years, or to use it as they pleased.

• Squamous-cell skin cancer: about 40% fewer tumours in the daily group. There was no effect on basal-cell carcinoma, the other common skin cancer.^[1]
• Melanoma: ten years on, the daily group had about half as many melanomas, 11 against 22. That result was only borderline statistically significant.^[2]
• Skin aging: in participants under 55, measured skin aging was about 24% less.^[3] See Photoaging.

All of this comes from one trial with small numbers of cancers, so treat the exact figures loosely. The direction makes sense, though. Squamous-cell skin cancer tracks the total UV dose your skin has taken, so cutting everyday exposure that never reaches a burn cuts it too.

Does it block vitamin D?

A little, at high SPF.

• Older randomised trials of daily sunscreen at around SPF 16 found no effect on vitamin D levels.^[4]
• A 2025 pooled analysis that mixed study types pointed to a small drop.^[5]
• The first randomised trial of a high-SPF product found that daily SPF 50+ left blood vitamin D (25-hydroxyvitamin D) about 5 nmol/L lower than in the control group over a year. More people ended up below the deficiency threshold: 45.7% against 36.9%.^[6]

So "sunscreen causes vitamin D deficiency" is overstated: most low vitamin D comes from indoor lifestyles and high latitude. Regular high-SPF users simply have one more reason to take oral vitamin D through the winter; see Vitamin D.

Who should use it, and when

A 2024 Australian position statement sorts adults into three groups:^[7]

1. Very high skin-cancer risk: very pale skin (Fitzpatrick types I–II), a weakened immune system, a history of melanoma, or many atypical moles. Protect from the sun year-round and get vitamin D from supplements.
2. Very dark skin (Fitzpatrick types V–VI): high risk of vitamin D deficiency and low skin-cancer risk. Routine daily sunscreen during ordinary outdoor activity is discouraged, and brief unprotected sun for vitamin D is appropriate.
3. Everyone else: everyday sun short of reddening, with sunscreen for longer stretches outdoors and when the UV index is high.

What sunscreen doesn't do

It is one layer, not the whole plan. A hat, long sleeves and UV-blocking sunglasses cut UV to the skin and eyes. Avoiding sunburn remains the single most useful rule. No sunscreen makes a tanning bed safe. The wider trade-offs, including how few minutes of sun make vitamin D, are on Sun exposure.

What to do

1. Long stretches outdoors: broad-spectrum SPF 30–50, or 50+ for very fair skin or a melanoma history, on everything that's uncovered.
2. Very pale skin, melanoma history, many atypical moles or a weakened immune system: use it year-round and take vitamin D orally.
3. Very dark skin: daily sunscreen for ordinary errands isn't needed; use it for long outdoor stretches.
4. Daily high-SPF users: take oral vitamin D through the winter.

Further reading

• Green A et al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet 1999.^[8]
• Green AC et al. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol 2011.^[9]
• Hughes MC et al. Sunscreen and prevention of skin aging: a randomized trial. Ann Intern Med 2013.^[10]
• Tran V et al. Effect of daily sunscreen application on vitamin D: findings from the open-label randomized controlled Sun-D Trial. Br J Dermatol 2025.^[11]
• Neale RE et al. Balancing the risks and benefits of sun exposure: A revised position statement for Australian adults. Aust N Z J Public Health 2024.^[12]