SPF15, SPF30, SPF50, UVA, UVB, UVC  – What does it all mean?

SPF15, SPF30, SPF50, UVA, UVB, UVC – What does it all mean?

Posted by Angela - Naturally Safe Cosmetics on 8th Aug 2019

These days, we see the letters SPF everywhere, not just on our sunscreen products but other items like facial moisturisers and cosmetics, too.

So what is SPF?

SPF stands for Sun Protection Factor and is a measure of the level of UVB protection a product provides for your skin. That level is indicated by the numbers which follow the letters SPF, for example, SPF15, SPF30 and SPF50. What do those numbers mean? Well, if your skin normally starts to burn after ten minutes in the sun, then an SPF30 sunscreen would increase that time-frame by a factor of 30, i.e. 30 x ten minutes = 300 minutes. Of course, it is important to remember that the actual level of protection, whether you burn and how long it takes before your skin starts to burn can be affected by other factors too, including:

  • your particular skin type
  • whether you are doing physical activity (causing you to sweat) while in the sun
  • swimming and towel drying
  • how much sunscreen you apply
  • how well you apply your sunscreen

How much of the Sun’s rays are blocked out?

No product will block out 100% of the sun’s UVB rays. Generally speaking:

  • SPF15 will filter out around 93% of UVB rays
  • SPF30 will filter out around 97% of UVB rays
  • SPF50 will filter out around 98% of UVB rays

As you can see, an SPF30 product does close the gap by a few more percentage points over SPF15, but SPF50 doesn’t make a lot of difference above SPF30.

Image source: Canva

What are the different types of rays?

UV radiation is classified into 3 types: UVA, UVB and UVC.

UVA rays:

  • are long wave ultraviolet rays
  • account for up to 95% of the UV radiation reaching the Earth’s surface
  • can penetrate clouds and glass
  • penetrate the skin more deeply than UVB rays
  • are responsible for immediate tanning and play a role in skin ageing (photoageing) and wrinkling

In the past, UVA was not believed to cause significant damage to the epidermis (the outermost skin layer). More recent research, however, indicates that UVA can cause damage to skin cells called keratinocytes in the basal layer of the epidermis where most skin cancers occur. This suggests that it can indeed enhance the development of skin cancer.

UVB rays:

  • are short wave ultraviolet rays
  • do not penetrate beyond the superficial layers of the skin
  • are responsible for skin reddening, sunburn and delayed tanning
  • play a key role in skin cancer development

The intensity of UVB rays can vary by season, location and time of day but they are usually at their strongest in the middle of the day, e.g. roughly between 10 a.m. and 2 p.m.

UVC rays:

  • are the shortest rays
  • are absorbed by the ozone layer and do not reach the Earth’s surface

A word about sunscreens

There are generally two types of sunscreens, both of which can protect your skin from the Sun's rays:

  • chemical sunscreens – designed to absorb and dissipate UVA/UVB rays. Unfortunately, they can contain ingredients which scientific studies have shown to be potentially harmful to humans. This includes ingredients like Oxybenzone and Octinoxate (with concerns about biochemical or cellular level changes, plus endocrine disruption) and Avobenzone (which can break down and lose its effectiveness in sunlight - how ironic is that?).
  • physical sunscreens (also called natural or mineral sunscreens) – designed to deflect and scatter UVA/UVB rays. These usually contain Zinc Oxide as their active ingredient. They sit on top of your skin creating an immediate physical barrier to the Sun’s rays.

When choosing sunscreen, look for a sunscreen that offers protection from both UVA and UVB rays, usually referred to as ‘broad spectrum’ protection, and make sure that it has a minimum SPF of 15. Also, be sure to apply your sunscreen before you go out into the sun, apply sufficient sunscreen and apply it all over exposed skin.

What about moisturisers and cosmetics with SPF?

More and more, we are seeing daily facial moisturisers with SPF. Of course, you can simply use your regular sunscreen on your face each day, with or without makeup. Even if you don’t spend a lot of time outdoors, per se, daily use of an SPF moisturiser on your face protects it from incidental damage that can occur when you go about your normal day to day activities, e.g. walking to work or the bus stop, stepping out for a sandwich during your lunch break. And, as mentioned above, UVA rays can penetrate glass (think driving in your car with the sun coming through the front windscreen, which is not allowed to be tinted, or sitting up against an untinted window in a building).

Most people prefer to have a lighter texture when it comes to their face moisturiser. This is why many SPF facial moisturisers made with Zinc Oxide have an SPF of 15 rather than 30 or higher. If more zinc was added, it would give a higher SPF rating but would potentially result in a thicker, whiter looking product which is not popular for use on the face. And when you consider that SPF30 only provides 4% more UVB protection, it’s probably better to have a lighter textured product which people are more likely to use every day.

Similarly, many cosmetics, especially mineral makeup (both powder and liquid) contain Zinc Oxide or Titanium Dioxide which gives the product a level of SPF – usually around 15-20 - check the label.

Disclaimer: The author and Naturally Safe Cosmetics are not health professionals. Any information or advice in this article is of a general nature only and not intended to diagnose, treat, cure or prevent any disease. For medical advice regarding your own personal circumstances, we recommend you contact your GP or other healthcare professional.

Sources:; World Health Organisation;