Sunscreen ingredients decoded — what the labels actually mean.

Sunscreen is the single most evidence-supported preventive step in skincare. The research on photoprotection — across skin ageing, pigmentation, and skin cancer prevention — is more consistent and more conclusive than the evidence for any other topical product. And yet sunscreen remains widely misunderstood, particularly around what the labels mean and what the ingredients actually do.

The two types of UV radiation

Ultraviolet radiation reaching the earth's surface comes in two relevant wavelengths.

UVA (320–400nm) penetrates more deeply into the dermis. It is responsible for the majority of photoageing — collagen degradation, elastin breakdown, pigmentation. UVA intensity is relatively stable throughout the day and across seasons; it penetrates glass. It is the radiation primarily responsible for cumulative, long-term skin damage.

UVB (280–320nm) is the primary cause of sunburn and plays a significant role in skin cancer development. UVB intensity varies substantially with time of day, season, and latitude. It does not penetrate glass as effectively as UVA.

A sunscreen that protects against only one type offers incomplete protection. Broad-spectrum coverage across both UVA and UVB is the requirement.

What SPF measures

SPF — Sun Protection Factor — measures protection against UVB only. An SPF 30 sunscreen, applied correctly, transmits 1/30th of the UVB radiation that would otherwise reach the skin. SPF 30 blocks approximately 97% of UVB; SPF 50 blocks approximately 98%. The difference between SPF 30 and SPF 50 is real, but modest.

The SPF number communicates nothing about UVA protection. A high-SPF product that lacks UVA filters — particularly in markets where UVA testing standards are less stringent — offers high UVB protection and inadequate long-term photoprotection.

The PA+ rating system

The PA+ rating (Protection Grade of UVA) originated in Japan and is now standard across much of East Asia and increasingly common globally. It is based on the Persistent Pigment Darkening (PPD) test, which measures UVA protection directly.

PA+ indicates UVA protection factor of 2–4. PA++ is 4–8. PA+++ is 8–16. PA++++ is 16 and above. A product rated PA++++ at SPF 50 is providing meaningful broad-spectrum protection.

In markets without a PA rating requirement — including Australia — UVA claims are assessed differently. The Australian TGA requires that a broad-spectrum sunscreen demonstrate UVA protection to a PPD of at least one-third of the SPF value.

Mineral filters (physical UV filters)

Zinc oxide (ZnO) reflects and scatters UV radiation across both UVA and UVB wavelengths. It offers inherently broad-spectrum protection from a single ingredient, is photostable, and is considered the lowest-irritation UV filter available. At higher concentrations, it produces white cast — a cosmetic limitation that newer formulations, including micronised and nano-zinc preparations, have largely addressed.

Titanium dioxide (TiO₂) reflects primarily UVB and shorter UVA wavelengths. It does not cover the full UVA spectrum the way zinc oxide does. Titanium dioxide is typically used in combination with zinc oxide or chemical filters to achieve full-spectrum coverage.

Mineral filters are typically recommended for reactive, sensitive, or compromised skin, and for children.

Chemical filters (organic UV filters)

Chemical filters absorb UV radiation and convert it to heat. They are typically lighter in texture than mineral formulations, more cosmetically elegant, and generally more effective per gram of filter. Their limitations are photostability — some degrade under UV exposure and must be stabilised by other filters or formulation chemistry.

Key approved chemical filters vary significantly by market:

Avobenzone is the most common UVA filter in the US market. It absorbs UVA effectively but is photounstable — it degrades on UV exposure unless stabilised. Modern formulations stabilise it with octocrylene, Tinosorb S, or other stabilisers.

Tinosorb S (bisoctrizole) and Tinosorb M (bemotrizinol) are broad-spectrum filters approved in the EU, Australia, and many Asian markets that cover both UVA and UVB and are highly photostable. They are absent from the US market, where FDA approval for new UV filters has been stalled for decades — creating a meaningful gap between US formulations and those available internationally.

Mexoryl SX and XL (ecamsule) are high-performance UVA filters developed by L'Oréal, approved in Canada, Europe, and Australia.

Application

The SPF value on a sunscreen label is achieved at a specific application density: 2mg per square centimetre of skin. For the average adult face, this is approximately a quarter teaspoon — far more than most people apply. Studies consistently show that real-world application averages 25–50% of the required amount, which reduces effective SPF protection to approximately the square root of the labelled value. SPF 50 applied at half the required density provides effective protection closer to SPF 7.

Reapplication every two hours in sun-exposed conditions is standard guidance. Water-resistant formulations maintain their SPF rating after 40 minutes of water exposure; water-resistant formulations at the higher resistance standard maintain protection after 80 minutes.

Choosing a sunscreen

For daily use on non-reactive skin, an SPF 30–50 broad-spectrum sunscreen with a texture you will consistently apply is the correct choice. A product you use every day at adequate quantity outperforms a theoretically superior product applied inadequately.

For reactive or sensitive skin, a zinc oxide-based mineral formulation at SPF 30 or higher provides reliable broad-spectrum protection with the lowest likelihood of irritation.

The Lux & Glo position

Sunscreen is not part of the Lux & Glo three-step ritual because the ritual is designed for evening use — and sunscreen, applied in the evening, provides no benefit. The three-step ritual is a skincare foundation; sunscreen is a prerequisite that belongs before it in the morning.

Consistent daily sunscreen use — at SPF 30 or higher, broad-spectrum, at sufficient quantity — is the most impactful single habit for long-term skin health. It precedes everything else.