How to choose a sunscreen: SPF and filter type

Sunscreen is one of the best documented steps in skin care. It reduces burning, slows the build-up of lines and pigmentation over time, and plays a part in lowering skin cancer risk. Even so, most people get confused at the shelf, because a tube carries a pile of markings whose relationship to one another is not immediately obvious: a number, letters inside a circle, filter names, a water resistance claim and texture promises. In this article we unpack those markings one by one, say which of them genuinely changes a decision, and explain how to choose according to your skin type. By the end, the places to look when you pick up a tube will be clear.

What does the SPF number measure?

SPF is a laboratory measured indicator of protection against UVB, the rays responsible for the sun's burning effect. Protection does not rise in a straight line as the number grows, and this is the most misunderstood part of the subject. SPF 15 blocks about 93 per cent of UVB, SPF 30 about 97 per cent and SPF 50 about 98 per cent, so the gain from moving from 15 to 30 is clearly larger than the gain from moving from 30 to 50. That does not mean a high SPF is pointless. The upper step is meaningful for people who stay outdoors for long stretches and for fair skin. But this sentence holds in every situation: an SPF 50 applied too thinly gives less protection than a generously applied SPF 30. Raising the number does not make up for a gap in application habits.

Why does the UVA mark inside a circle matter?

As the name suggests, SPF measures only the ray associated with burning. Yet there are also UVA rays, which can largely get past glass and cloud cover and which reach deeper without burning, contributing over time to loss of elasticity and uneven tone. That is why you look for a marking showing UVA protection next to the SPF number. On products sold in Europe that marking is the letters UVA inside a circle, which shows the product's UVA protection meets a set proportion of its SPF value. On some products you will see a broad spectrum statement instead, and on products of Asian origin the PA system shown with plus signs. Whichever notation appears, the logic is the same. You are looking for protection against both types of ray, not just one.

Mineral and chemical filters: which suits whom?

Filters fall broadly into two families. The mineral ones are zinc oxide and titanium dioxide; they stay on the outermost surface of the skin and meet the rays largely there. Chemical filters are molecules in the formula that absorb light and convert its energy into heat. Neither family is absolutely superior. The difference shows up not in protective strength but in comfort of use and tolerance profile. Mineral filters have a low irritation potential and are therefore often suggested for sensitive skin and for children, though they can leave a white cast problem on deeper skin tones. Chemical filters give a more transparent, lighter finish and sit more comfortably under make-up, but some can sting or redden reactive skin. We explain the role of titanium dioxide in cosmetics, and how that differs from its status in food, on our ingredient page.

On a label you see the filters in the ingredient list under their INCI names: Zinc Oxide, Titanium Dioxide, Butyl Methoxydibenzoylmethane, Octocrylene, Ethylhexyl Triazone and so on. Mineral filters may carry the word nano in brackets. This is regulatory information stating the particle size, not a warning on its own. It is also common for one tube to contain both mineral and chemical filters, and that is not an inconsistency but a deliberate formulation choice made to achieve broad protection.

How to choose by skin type

Two products at the same protection level can feel completely different on two different skins, and the reason is texture. A sunscreen you do not use provides no protection at all, so comfort here is not decoration but a matter of effectiveness. The table below summarises where to look according to your skin type.

Sensitivity is a separate heading here. On reactive skin irritation often comes not from the filter but from the other components of the formula, with the fragrance blend at the top of that list. On our fragrance ingredient page we explain how fragrance allergens appear on a label. For building a daily routine, see our sensitive skin care guide. If pore clogging is on your mind, the article on what comedogenic means explains that the concept is less absolute than people assume.

Quantity: the most skipped step

The SPF value on the label is measured assuming a standard application quantity, and in daily life most people apply considerably less. The protection actually obtained falls noticeably below the number on the tube. A practical measure for the face and neck is two strips of product laid along the index and middle fingers. That is roughly a quarter of a teaspoon. The ears, the sides of the nose, the outer edges around the eyes, the hairline and the back of the neck are the most frequently skipped areas. If you stay outdoors for a long time you need to reapply every two hours, and sweat, towel contact and going into water shorten that interval. Even products carrying a water resistance claim are not limitless. They are tested for a set period, and the reapplication rule still applies once you leave the water. The body needs counting in as well as the face: on a day spent in swimwear, covering every exposed area takes roughly a small glass full of product, around thirty millilitres. That amount strikes most people as excessive, and that is precisely why it is under-applied in practice. One way to stop the quantity feeling daunting is to apply the product in two thin layers rather than spreading it all at once. The second layer both covers the spots you missed and raises the total amount.

Its place in the routine: when and in what order?

A sun product goes on at the very end of the morning routine, over your care steps. If you have applied a moisturiser, waiting a short while for it to absorb reduces the layers mixing into each other and prevents pilling. If you wear make-up, the protective layer goes underneath it. Reapplying during the day is the hardest point on a made-up face. The practical answer here is a spray or powder format as a top-up rather than reapplying a fluid product, though it is worth remembering that these too need to go on in sufficient quantity. Another practical point is the eyes. Some formulas sting when they run into the eyes with sweat, in which case a better tolerated texture for the eye area, or physical support such as sunglasses and a hat, makes life easier.

Storage conditions are part of effectiveness too. Since high temperatures can upset the balance of a formula, the product should not be left in a car or in direct sun at the beach; the shaded side of a bag or under a towel is better. How long an opened pack can be used is written in the open jar symbol on the box. In most products that period varies between twelve and twenty four months. Before using a half-empty tube left over from last summer, it is sensible to check both that period and whether there has been any change in the product's smell, colour or consistency. A product that has separated, turned grainy or changed in smell may not deliver the protection you expect.

Widespread misconceptions

A few beliefs circulating around this subject lower the protection even of people who chose the right product. Many assume there is no need for protection on a cloudy day, whereas UVA passes through a significant part of the cloud layer. Others think there is no issue behind glass. Glass holds back most UVB, but the same cannot be said for UVA, which makes long car journeys and desk hours by a window relevant. The SPF value in make-up products is assumed to be enough. Because these are applied far below the measurement quantity, they do not count as protection on their own. Then there is the promise of protection from within. The claim that foods and supplements containing beta carotene or similar components can replace sunscreen is not supported by evidence, and it does not take the place of protection applied to the skin.

Who does this matter most to?

• Fair, freckled people who burn easily: because their burning threshold is low, an upper protection step and regular reapplication make a bigger difference here.
• People dealing with pigmentation and uneven tone: light is one of the strongest triggers of darkening, so protection counts as an inseparable part of treatment.
• People using actives such as acids and retinol: since these components can make skin more sensitive to light, daytime protection is a required step in the routine.
• People working outdoors and those exercising regularly: sweat and friction shorten the reapplication interval, so a practical way to carry the product is needed.
• Children: their skin is thinner and cumulative exposure starts building early; shade and clothing are part of protection at this age too.
• People taking medicines that can cause light sensitivity: in that case personal advice should come from your doctor or pharmacist.

Common mistakes

• Treating a high SPF as grounds for applying once and forgetting it all day: the number describes the proportion of protection at that moment, not a duration.
• Saving the product for summer months and holidays: light exposure continues through most of the year and in the city too.
• Leaving the cream in a car glovebox or in a beach bag under the sun; high temperatures can upset the balance of the formula.
• Using last year's half-empty tube without checking its date: protection depends on the integrity of the formula.
• Applying only to the face and forgetting the neck, ears and backs of the hands; these are the areas where the difference becomes most visible over time.
• Spreading a product very thinly because it leaves a white cast: that directly lowers the amount of protection, and changing the product is the better answer when a texture does not suit you.

A 30 second check at the shelf

• Is the SPF value at least 30, and is there a higher step if you are outdoors for long periods?
• Is there a UVA mark inside a circle, or an equivalent broad spectrum statement?
• Which filters are in the ingredient list: mineral, chemical, or both together?
• If you are buying for sensitive skin, does a fragrance blend appear on the list?
• Is there a water resistance claim, and does it suit the activity you have in mind?
• When you cannot decide between two tubes, scan them and compare their filters, fragrance status and suitability for your skin type.

Summary

The right sunscreen is not the most expensive one or the one with the highest number. It is the one you will keep applying every day. The decision comes out of three questions: is the protection level sufficient, are both types of ray covered, and do the texture and formula suit your skin? Once those three are settled, what remains is habit: a sufficient quantity, including the areas that get skipped, and reapplying when needed. If you want to clarify what to look for according to your skin type, have a look at product analysis by skin type. This article is general information; if you notice a change in a mole, a wound that does not heal, or an unusual reaction to light, you should have it assessed by a doctor.