The skincare market is enormous and the evidence supporting most of it is modest. Sunscreen is the clear exception, with randomised controlled trial evidence for outcomes that matter.

What the trials found

A landmark randomised trial in Australia assigned adults to daily sunscreen use or discretionary use and followed them for years.

The findings included a reduction in squamous cell carcinoma incidence in the daily use group. Extended follow-up also reported a reduction in melanoma incidence.

A separate analysis from the same trial examined skin ageing, and found that the daily sunscreen group showed significantly less skin ageing over the follow-up period than the discretionary group.

That's an unusual thing to have — randomised evidence that a cosmetic intervention prevents visible ageing. Most anti-ageing claims rest on considerably less.

Why UV matters

Two wavelength ranges reach the skin and do different things.

UVB is largely responsible for sunburn and directly damages DNA, contributing to skin cancer development.

UVA penetrates deeper, contributes to photoageing through effects on collagen and elastin, also contributes to cancer risk, and passes through window glass.

That last point matters practically: UVA exposure continues indoors near windows and while driving, which is a genuine and underappreciated source of cumulative exposure.

Reading the labelling

SPF measures protection against UVB specifically. It relates to the amount of UV required to cause erythema with and without the product.

The relationship isn't linear in the way people assume. SPF 30 blocks around 97% of UVB; SPF 50 around 98%. The difference in absolute terms is small.

What matters more is that SPF is measured at an application density considerably higher than most people use. Studies of real-world application consistently find people apply substantially less than the test amount, which means the protection achieved is meaningfully lower than the label figure.

Applying a higher SPF partly compensates for under-application, which is a practical argument for choosing higher numbers despite the small theoretical difference.

UVA protection is labelled differently by region — a star rating, a circled UVA symbol, or a separate rating system depending on where you are. Checking for a UVA indication as well as SPF is worth doing.

Application

Where most of the benefit is lost.

The recommended quantity for the face and neck is roughly a teaspoon, which is considerably more than most people apply. For the whole body it's around a shot glass.

Reapplication every two hours during sun exposure, and immediately after swimming or heavy sweating regardless of water-resistance claims.

The commonly missed areas: ears, back of the neck, hands, the tops of the feet, the scalp along a parting, and the eyelids.

Under makeup is fine, and reapplication over makeup is the practical problem. Powder or spray formats designed for this exist and deliver less than a proper reapplication.

Mineral versus chemical

Two broad categories, and the distinction is less important than the marketing suggests.

Mineral filters — zinc oxide and titanium dioxide — sit on the skin and are generally well tolerated by sensitive skin. Historically they left a white cast, which modern formulations have substantially reduced though not eliminated on deeper skin tones.

Organic filters absorb UV and convert it to heat. They tend to be cosmetically more elegant and a wider range is available in some regions than others due to differing regulatory approval.

Both work. Concerns about systemic absorption of certain organic filters have been raised, and regulators have generally maintained that they remain appropriate for use while requesting further data. The established benefit in cancer prevention is considerably better characterised than any hypothesised risk.

The vitamin D question

A common and reasonable concern, since UVB exposure drives vitamin D synthesis.

Studies examining vitamin D levels in people using sunscreen regularly have generally not found clinically significant deficiency attributable to it, likely because real-world application is imperfect enough to permit some synthesis.

Where vitamin D status is a concern, supplementation is a straightforward solution that doesn't require accepting UV damage. That's the recommendation most dermatology bodies make.

What else has evidence

Briefly, since sunscreen isn't the only thing that works.

Retinoids have good evidence for photoageing and are the other genuinely well-supported topical category.

Moisturisers improve barrier function and the appearance of fine lines, straightforwardly.

Beyond that, evidence thins rapidly. Many ingredients have plausible mechanisms and cell culture data, with limited clinical trial evidence in humans at the concentrations used in products.

Which is a reasonable argument for a simple routine: sunscreen daily, a moisturiser suited to your skin, and a retinoid if you want to address ageing specifically. That's most of the available benefit, and the rest of a large industry is competing for the remainder.

General information only. Anyone with a skin condition, or concerns about a specific lesion or mole, should consult a healthcare professional.

What sunscreen does not replace

Worth stating because sunscreen use can produce a false sense of complete protection, and there is some evidence that people who apply it stay out longer as a result.

Shade, timing and clothing all provide protection that does not depend on correct application or reapplication. Avoiding the hours around solar noon, wearing a wide-brimmed hat, and using clothing with a tight weave are all more reliable than a product applied at a quarter of the tested density.

The sensible approach uses all of them together, with sunscreen covering the areas clothing does not. It is also worth checking moles periodically and knowing what changes warrant attention: asymmetry, irregular borders, colour variation, size, and any change over time.