No sunscreen can provide 100% UV protection

First published June 2017; updated May 2019

The role of sunscreen
Alongside other protective measures, such as clothing and shade, sunscreens play an important preventative role against the acute and long term effects of overexposure to ultraviolet (UV) radiation from the sun, including: sunburn, skin damage, premature ageing of the skin and skin cancer.

Solar UV radiation
UV radiation is a component of sunlight and is divided into three categories, classified according to wavelength: UVA, UVB and UVC. The ozone layer blocks all UVC, so we only need to protect ourselves against UVA and UVB.

UVA rays penetrate more deeply through the layers of the skin than UVB. UVA is present year round, even on cloudy days and can pass through window glass. It is associated with skin ageing as well as skin cancer.

UVB rays are mainly responsible for sunburn, can’t pass through window glass and are strongly associated with two types of skin cancer – malignant melanoma and basal cell carcinoma. Learn more about UV here. 

Sunscreens: how they work
Sunscreens help to protect our skin by filtering out UV radiation through the use of chemical (organic*) and physical (inorganic) active ingredients. Chemical filters absorb UV radiation, while physical filters (e.g. titanium dioxide or zinc oxide) reflect UV radiation.

*In this context, the term organic does not mean ‘natural’ or ‘additive-free’ but is a word used by scientists to describe molecules containing carbon atoms.

Sunscreens act like mirrors or sponges
A handy way to think about it is that physical sunscreens act like a mirror and reflect UV radiation away from the skin, while chemical sunscreens act like a sponge and absorb UV radiation.

Understanding sunscreen labelling
SPF stands for Sun Protection Factor and shows the degree of protection the sunscreen provides against UVB only. It is rated on a scale from 2-50+. The higher the factor, the greater the level of protection against UVB.

UVA Star ratings range from 0-5, and indicate the level of protection the sunscreen provides against UVA, compared with the level of protection it provides against UVB (i.e. the ratio between the level of UVA and UVB protection offered by the product). The higher the number of stars, the greater the level of protection against UVA.

Sunscreens with a low SPF can still have a high number of stars, not because they are offering high UVA protection, but because the ratio between UVA and UVB protection is the same as offered in sunscreens with higher SPF. This is why it is very important to choose a sunscreen with a high SPF as well as high UVA protection (ideally 4 or 5 stars).

The EU recommends that the UVA protection offered in a sunscreen should be at least one third of the SPF. Sunscreen products meeting this requirement are eligible to display a UVA logo, with the letters UVA enclosed within a circle.

Open jar / period-after-opening symbol
An ‘open jar’ symbol located on the sunscreen container indicates the period of time after the product is first opened, that it is safe to use (i.e. there is no decrease in the effectiveness of the sunscreen).

This ‘period after opening’ is usually specified in months (often abbreviated to M, e.g. 12 M) or years, and located within or just beside the open jar symbol. The manufacturer’s storage instructions should also be followed.

Choice of sunscreen
The British Association of Dermatologists (which works closely with the Irish Association of Dermatologists) recommend ‘high protection’ broad-spectrum sunscreens (offering protection against UVA and UVB), with an SPF of at least 30 and high UVA protection, in addition to protective clothing and shade.

‘More is better’
While individual manufacturers provide instructions specific to their products, an average sized adult requires at least 36 grams of sunscreen (about six full teaspoons) to cover their body and achieve the protection indicated on the label – this is the amount used when products are tested to measure their SPF, calculated on the basis of applying 2mg of sunscreen per square centimetre of skin.

Many people don’t realise that applying less than the recommended amount may reduce the protection which a sunscreen provides to a higher degree than you would think is proportionate, e.g. only applying half the required amount can reduce the protection by a shocking two-thirds.

When to apply and reapply
Sunscreen should be applied liberally and evenly 15-30 minutes before sun exposure to allow it time to dry, and again shortly after going outdoors to ensure that all areas are covered. Reapply frequently, at least every two hours and after perspiring, sport, swimming, or friction (such as towel drying).

An Irish context
In Ireland, make sun protection part of your daily routine particularly from April to September, when the intensity of sunburn producing UV radiation is greatest. But remember, whether at home or abroad, if the UV index is 3 or above, sun protection is required.

Know your skin type
A person’s natural skin colour influences their risk of skin cancer so sun-safe recommendations (protective clothing, shade and sunscreen) should be used alongside information on skin type, providing a better sense of the care you need to take: know your ‘skin type’. Learn your skin type here. 

The Vitamin D debate
Vitamin D is important to keep teeth and bones healthy. Dietary sources of vitamin D include oily fish and fortified foods. Your body also produces vitamin D during short periods of incidental sun exposure. Vitamin D produced in the skin is ‘biologically regulated’ – long periods of sun exposure can actually break it down, consequently reducing benefit and increasing risks of cancer.

So the advice from dermatologists is to get some sunshine as you go about your day to day activities without burning or deliberately tanning. Vitamin D supplements are sometimes required by those at risk of low levels, for example: pregnant and breastfeeding women, young children, older people, and those with darker skin.

A higher price doesn’t necessarily indicate better protection.

What to look for
Look for ‘high protection’ broad spectrum sunscreens, with an SPF of at least 30 + for adults /50+ for children, and a UVA circle logo and/or 4 or 5 UVA stars.

The Health Products Regulatory Authority advises that sunscreens should only be bought from a reputable source. In this way, the product can be traced back to the supplier. It also recommends checking the label of the sunscreen for a European address – if a product has been imported from outside the EU, it may not meet European safety assessment requirements.

Remember the 5 ‘Ss’ of sun safety:

  • Slip on clothing: Cover skin as much as possible e.g. wear long sleeves, collared t-shirts, clothes made from close-woven material that does not allow sunlight through.
  • Slop Slop on broad-spectrum (UVA/UVB) sunscreen with a sun protection factor (SPF) of at least 30+ for adults and 50+ for children, with high UVA protection, and water resistant. Reapply regularly.
  • Slap on a hat with a wide brim: Protect your face, ears and neck.
  • Slide on sunglasses with UV protection: Guard your eyes from harm.
  • Seek shade: Sit in cover of trees to avoid direct sunlight and use a sunshade on your buggy or pram. Keep babies and children out of direct sunlight.

We want everyone in Ireland to learn to Protect & Inspect their skin! Read our short guide, written with hospital-based dermatologists, to checking your skin.   

Click for more about Protect & Inspect!