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How to choose and use a sunscreen

Author: Dr Louise Reiche, Dermatologist, 2007. Updated by Vanessa Ngan, Staff Writer, August 2012.



Improved knowledge related to the sun and technology advances has made sunscreen issues more complex. Which sunscreen product is most suitable depends on many factors such as how sensitive the skin is to burning and cosmetics, how dry or oily the skin is, previous sun and skin cancer history and medical history.

Why use a sunscreen?

Sunscreen is mainly used to protect the skin against ultraviolet radiation, which damages the skin.

Sunlight generates warmth (infra-red) that we can feel, visible light (that our eyes can see in daylight) and ultraviolet light (UVL) which we cannot see or feel but which can penetrate our skin.

  • The UVL that reaches the earth is grouped into shorter UVB and longer UVA wavelengths.
  • Our skin makes Vitamin D from small amounts of UVB, but larger amounts of UVB may cause sunburn and contribute to skin cancers.
  • UVA penetrates deeper and large, or prolonged exposure may also cause burning, premature skin ageing and skin cancers.
  • Both UVA and UVB suppress skin immune function.

For these reasons, sun protection is strongly recommended throughout our lifetime.

Sunscreens do not provide total protection and should be used in conjunction with other sun protective measures such as wearing sun protective clothing and staying indoors or out of the sun during peak sunshine hours.

What sunscreen should I choose?

Sunscreen products protect the skin by absorbing and blocking harmful UVL. See topical sunscreen agents for a list of the active ingredients that make up the many sunscreen preparations available. All sunscreen products must be tested, classified and labelled according to their sun protective capabilities (see sunscreen testing and classification).

SPF for UVB protection

SPF stands for sun protection factor. This tells us how much longer we could expect to be exposed to UVB before burning compared to no sunscreen. For example, if it takes 10 minutes to burn without sunscreen and 150 minutes to burn with sunscreen, the SPF of that sunscreen is 15 (150/10).

  • The higher the SPF number, the better is the expected protection.
  • A sunscreen with an SPF 15 provides about 94% protection against UVB.
  • Protection against UVB is increased to 97% with SPF 30 and increased to 98% with SPF 50+.

As you can see the difference in protection when going from sunscreen with SPF 15 to one with SPF 30 or even 50+ differs only by 3–4%. Also, this protection is only provided if sunscreens are applied in quantities similar to the ones used for testing, 2 mg/cm2. This is six teaspoons of lotion for the body of one average adult person.

  • In reality, most people apply their sunscreen at about one third the thickness used for testing.
  • They fail to apply it to all exposed areas of skin.
  • They forget to reapply it every couple of hours or after heavy sweating or swimming.

Therefore, the actual protection may be a lot less than the tests indicate.

A sunscreen with SPF 15+ should provide adequate protection as long as it is being used correctly. Sunscreens with SPF 50 or more offer a safety margin since most people don’t apply sunscreens as heavily or as often as they should.

Broad Spectrum for UVA protection

With increasing awareness about UVA-induced skin damage, it is important to choose a sunscreen that also protects against UVA radiation. These products are labelled with the statement “Broad Spectrum”. Always choose a sunscreen which has at least one of its ingredients that protects across the full UVA range. These include the metal oxides, titanium dioxide and zinc oxide, and the chemical absorbers, avobenzone, ecamsule, bemotrizinol and bisoctrizole.

The UVA protection factor (UVA-PF) must be at least 1/3 of the labelled SPF, so choosing a sunscreen with a higher SPF will also mean higher UVA protection.


Choose a sunscreen that is photostable to ensure that it will not breakdown and become ineffective on exposure to sunlight. Octocrylene, bemotrizinol and bisoctrizole are photostable agents and when combined with other chemical absorbing agents improve the overall photostability of the sunscreen product.

What sunscreen can I use?

Selecting a sunscreen depends on how sensitive your skin is to burning and cosmetics, the dryness or oiliness of your skin, previous sun and skin cancer history, and your general medical history.

  • If you have fair skin that burns easily, you should choose a high-SPF broad-spectrum sunscreen labelled as SPF 50+.
  • If you have skin that tans readily you could choose a sunscreen with an intermediate SPF of 15+.
  • If you have darkly pigmented skin and do not suffer from photosensitivity or abnormal pigmentation, you do not need sunscreen.

Sensitive skin

If you have sensitive skin that has trouble tolerating sunscreens or cosmetics, look for hypoallergenic/low irritant sunscreens. You may like to try a variety of sunscreen samples before deciding what you will use regularly. If you are still having rashes, you might have a sunscreen allergy and need to undergo allergy patch testing to identify a particular ingredient in sunscreens that is causing the problem.  

Dry or oily skin

  • If your skin is dry, you will benefit from sunscreen in a moisturising cream or ointment.
  • If you have oily skin or readily develop acne, choose a sunscreen in a lighter base, such as an alcohol-based lotion, spray or gel.
  • Lighter sunscreens are also better in hairy skin areas.
  • Sunscreen sticks are suitable for nose, lips and around the eyes.

During activity

If you plan to be active outdoors and may get wet or sweaty, choose a sunscreen that is labelled “water resistant”. These products should also show the amount of time you can expect to get the declared SPF level of protection while swimming or sweating, for example, SPF 15 – Water resistant 40 min.

How to use a sunscreen

  • It is essential to use sunscreen correctly to achieve the best protection.
  • Apply sunscreen liberally to all sun-exposed areas so that it forms a film when initially applied. Most people do not use enough. It takes at least six teaspoons of lotion to cover the sun-exposed areas of the body of one average adult person.
  • It takes 20–30 minutes for sunscreen to be absorbed by the skin and it can easily be rubbed off, so apply it at least half an hour before going out in the sun.
  • Reapply after half an hour so that the ‘mountains’, as well as the ‘valleys’, are protected (imagine you are painting a wall – two coats of paint provide a more even coverage than one).
  • Re-apply sunscreen every 2 hours if staying out in the sun for more than an hour during the day.
  • Re-apply immediately after swimming, excessive sweating, or if rubbed off by clothing or towelling, even if the product claims to be “water resistant”.
  • Insect repellents reduce the sunscreen's SPF so when using together, use a sunscreen with a higher SPF and re-apply more often.

What about vitamin D?

If you have fair skin, you may make enough vitamin D after only 5 minutes of midday summer sun activity when wearing shorts and T-shirt. It takes a little longer in dark skin. Usual recreational use of sunscreens does not lead to vitamin D inadequacy [1].

  • Being physically active outdoors helps you make more vitamin D than resting in the sun.
  • If you are over 50 years old (ageing skin is not as good at making vitamin D), immunosuppressed or have had previous skin cancers, you are better to apply sunscreen and take vitamin D supplements.



  1. Passeron T, Bouillon R, Callender V, Cestari T, Diepgen T, Green A, van der Pols J, Bernard B, Ly F, Bernerd F, Marrot L, Nielsen M, Verschoore M, Jablonski N, Young A. (2019), Sunscreen photoprotection and vitamin D status. Br J Dermatol. Accepted Author Manuscript. doi:10.1111/bjd.17992. Journal

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