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Sun Protection Factor (SPF) Explained

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The Australian sun has been getting hotter and hotter over the last century and by now most Australians have learnt that they should apply sunscreen every time they step out into the sun for any length of time longer than popping down to the local shops. What’s more we’ve become educated enough about the dangers of the sun that we now know we should wear SPF 30+ sunscreen or higher, but most of us probably don’t know exactly what that means. So what is SPF and how does it work?

What is SPF?

SPF stands for Sun Protection Factor, and it is a relative measure of the duration that a particular sunscreen will protect you from Ultraviolet B (UVB) rays. UVB rays are the main cause of sunburn and the main culprit for common types of skin cancer. This shouldn’t be confused with UVA rays which are longer and more likely to penetrate deeper into the body and cause internal damage to DNA cells. However, SPF is based on UVB rays, which vary in intensity throughout the day.

In order to understand this a little better we need to do a little bit of math. On a particularly hot day an individual might burn after 10 minutes of sun exposure. If they were using a sunscreen with SPF 15 on the bottle then they would burn after 150 minutes, or 15 times longer than they would without sunscreen. Similarly, if they were using SPF 30, they would burn after 300 minutes, or 30 times longer than without sunscreen.

It is really important to understand that this is a relative measure, which means that it is based on how long a person would take to burn without sunscreen. Which is dependent upon the person’s skin type, where they live, the intensity of the UV index on that day and many more factors. So it is not easy to calculate how long you can stay out in the sun before burning, only that SPF 30 sunscreen will protect you for twice as long as SPF 15.

What about UVA rays?

This is where it becomes really important to read the fine print on your sunscreen bottle. SPF protection only refers to UVB rays, so it is not a measure of whether or not it also blocks UVA rays. UVA rays can be just as dangerous to the body and cause darkening and aging of the skin, so it is important to ensure that your sunscreen also protects you from UVA rays. This is why looking for sunscreen that offers “Broad Spectrum” protection is so important, because this type of sunscreen will protect you from both types of electromagnetic radiation.
Proper sun protection

Sunscreen, even sunscreen with very high SPF, is still not enough to provide total protection from the sun. That’s why you should always ensure not only to apply sunscreen generously every two hours but also use a hat, shirt, sunglasses and search for shade in the middle of the day.

Applying sunscreen

The SPF of a sunscreen can be greatly reduced if the sunscreen is applied incorrectly. Adults should apply at least one teaspoon of sunscreen to each arm, leg, and front and back of body and at least ½ a teaspoon to the face, neck and ears. Sunscreen should be applied at least 20 minutes before going out into the sun and should be re-applied every 2-4 hours.

How it works

There are two types of sunscreens: physical and chemical.

  1. Physical (Titanium Dioxide or Zinc Dioxide)
    This type of sunscreen acts as a physical shield between the skin and sunlight. Until recently this type of sun protection, when applied, was opaque but a new scientific process called micronisation has allowed the particles to be broken down so small that when applied to the skin they become invisible.
  2. Chemical
    These types of sunscreen deactivate UV radiation that reaches the skin preventing damage caused by UV Rays.

WARNING! Sunscreen should not be used as a primary means of sun protection. The most important and effective method for avoiding skin cancer is avoiding the Sun, particularly during the hottest time of the day (between 11am and 3pm). Sunscreen should be applied to complement the use of protective clothing and hats, when sun avoidance is not possible.

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