Everything You Need to Know About SPF

For a lot of people, time spent in the sun is fun, carefree and the go-to option in the summer. But, as you were probably told so many times as a child, you do need to take care to protect yourself from the sun because it can be dangerous. There are a lot of issues that the sun can cause so you need to respect it by having the right kind of protection.

Besides making sure that you stay out of the sun during the really hot times, and wearing the right clothes, you need to gear up with the right sunscreen and make it count.

Understanding the Difference Between UVA and UVB

There are two different types of ultraviolet rays – UVA and UVB. They’re both just as harmful to your skin.

This specific type of ultra-violet ray makes up 95% of all UV radiation that reaches the surface of Earth. Whilst this is less intense than UVB, it is more plentiful, and has no issue penetrating both clouds and glass structures, and penetrates deeper into the skin.

This is the ray you get in a tanning booth, and prolonged exposure to it can cause long-term health issues like skin cancer.

UVB is what will be primarily responsible for sunburn and can play a significant role in the development of skin cancer. This particular type of ray is most prominent during the summer, but you will encounter it all year round. High altitudes are particularly common areas to find UVB, because the atmosphere is thin.

Your Guide to Sun Protection Factor (SPF)

So, what is SPF, and how does it affect your sun protection?  SPF gives an indication of how long it will protect the skin compared to not wearing any protection. Applying SPF30 properly would protect you for 30 times the average length, so in theory you would be able to stay out in the sun for 30 times as long as if you weren’t wearing any sun protection.  However, given that most people don’t apply enough sunscreen, it is not recommended that you stay out in the sun that long.

We recommended that you use at least SPF 30 as a minimum. This will give you the minimum level of coverage that you need. However, if you have fair skin or you have children, they should be using SPF 50 for extra protection. People who have a lighter skin tone have decreased protection on account of the lower amount of melanin in the skin, so will need a higher SPF.

You will need to make sure that you reapply your sunscreen on a regular basis, and that you make sure to cover areas that could be at particular risk, like ears and noses.


How Much Sunscreen is Enough?

You might not know this, but most people don’t actually use enough sunscreen. You need to aim for about 2 mg of sunscreen for each square centimetre of skin that you want to cover. So, this means that you need to apply about the equivalent of 2 tablespoons of sunscreen to all the exposed areas of the body. If you are using a spray sunscreen, then make sure there is an even coating all over the skin.

Description on bottle

SPF 30 cream

SPF 50 spray

Actual SPF when applied at:

Recommended levels (2mg/cm2)



Half recommended levels (1mg/cm2)



Quarter recommended levels (0.5mg/cm2)



Ou-Yang et al. , J Am Acad Dermatol. 2012

To try and put that into perspective, a 250ml bottle of sunscreen should last 10 applications for one person. Alternatively, a regular family would only get two applications each. But not many of us are using anything like as much as this, and we’ve all had bottles that have lasted longer than our holidays. On average people apply between a quarter and half the recommended amount. The table below shows the effect of using a thinner layer of suncream, and it’s surprising just how quickly the protection drops off.

On average, sunscreen will need to be re-applied roughly every two hours. However, you may need to do it more frequently if you perspire heavily, go swimming, or use a towel. You need to have at least SPF 30 for a reasonable level of protection, but if you’re going to spend a lot of time outdoors in direct sunlight, then go for something higher like SPF 50 or make sure to cover up!

You should also make sure that the product is capable of protecting you against both UVA and UVB rays, so you will be looking for sunscreen that says “broad spectrum”.

It’s probably important to recognise that nobody is going to get a perfect level of sunscreen, so there will be some parts of the body which have less protection than others. That is usually why you would go for a higher SPF such as SPF50, because it means that you get a reasonable amount of protection even if some areas of your body get a thinner level of sunscreen applied.

Avoiding skin cancer

Understanding how SPF works is vital for protecting your skin. You have to make sure that you are taking good care of yourself from beginning to end to avoid sunburn and prevent skin cancer.

The sun is not something to be taken lightly or messed around with, it is a very potent heat source that will cause you damage if you don’t properly prepare for it.  Unlike with smoking-related lung cancer, where you can reduce your risk by stopping smoking later in life, with skin cancer it doesn’t matter when you had your sun exposure. If you were burnt during your childhood, you will have significantly increased your risk of skin cancer, even if you have taken sensible precautions later in life.

SPF 30 is a minimum requirement regardless of your situation, and it is always recommended to go higher if you are planning a day at the beach. Remember to reapply regularly, don’t spend too much time in the sun, and do all the basic things like drink plenty of fluids and try to avoid the midday sun. All of these activities will help to protect you from the effects of sunburn and skin cancer, which go hand-in-hand.

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For more information, or to book an appointment with one of our dermatologists, please call the clinic or contact us.