Let There be Light: Let’s Talk About the Sun

Who doesn’t love spending a day in the sun? Many covet sun-kissed, tanned skin but most also know in this day and age the importance of sun protection. SPF should be your BFF.

I love saying, “Keep it simple and just wear sunscreen every single day!” But not everyone is convinced as to why that is such a good idea.

Surely not every day, right? I promise when you finish reading this piece, you will agree.

Let’s find out the difference between UVA and UVB, what SPF actually stands for, and if it matters if you wear physical or chemical sunscreens.

What is the difference between UVA and UVB rays?

We’ve all heard of ultraviolet (UV) radiation, the part of the spectrum of light that comes from the sun that doctors are all obsessed with. There are three types of UV light: UVA (400-320nm), UVB (320-290nm), and UVC (290-200nm).

For now forget UVC. This is the shortest wavelength of UV light and is filtered out by our atmosphere. We’re mostly concerned with UVA and UVB.

Have you ever heard of the general rule: "A is for Ageing and B is for Burning?"

This is an oversimplified way of looking at things, but it may help you remember the difference between the two!

The Science: We know intuitively that the intensity of the sun and the UV light our skin experiences varies and depends on a variety of factors. The position of the sun in the sky (its elevation on the horizon) will have an effect and is why at different times of the day, days of the year, and locations we feel the effect of the sun more or less strongly. The atmosphere plays a role in absorbing and scattering light, as well as cloud coverage. Finally sand, water, and snow can all reflect a great deal of sunlight back onto us.

UVA rays have a longer wavelength and can therefore penetrate more deeply into the dermis of the skin. This longer wavelength also allows UVA to penetrate cloud cover or through windows more easily. As this radiation is not the type that causes instant burning, we don't tend to see the damage that UVA radiation is causing until a little further down the line when our skin begins to wrinkle and gain sun damage and pigmentation. UVA also tends to remain fairly constant throughout the day, so there is a continuous exposure to it.

UVB rays have a shorter wavelength and therefore penetrate more superficially into the epidermis of the skin. They can also be filtered out by glass. They cause the immediate damage that we see in sunburns. UVB peaks in the middle of the day (as you would expect).

What is the truth about having a tan?

At the end of the day, there is no such thing as a healthy tan. Even though to some people it might look nice, a tan just signals that your skin has been damaged by UV radiation and has produced more pigment in an attempt to protect itself.

You skin reacts differently to UVA and UVB rays. UVA will activate the melanin that is already in your skin, creating an initial tan very quickly. This tan will disappear just as quickly.

UVB causes your skin cells to produce brand new melanin, and this increase in pigment will not appear right away. This creates a tan that shows up a few days after sun exposure, and lasts longer.

What is the difference between physical (inorganic) and chemical (organic) sunscreen?

Physical (inorganic) sunscreens contain minerals like zinc oxide, and they protect the skin by absorbing the UV radiation and turn it into heat, dispersing it from the skin. They also create a light-reflecting layer on its surface to deflect sun rays (only about 10%). People with sensitive skin may prefer physical sunscreens, but they can sometimes leave skin with a white, chalky sheen that some may dislike!

Because there are fewer ingredients in physical sunscreens, they are often preferred by medical-grade skincare brands.

Chemical (organic) sunscreens also absorb UV radiation and turn it into heat, so work in exactly the same way to physical sunscreens in this regard. Chemical sunscreens tend to give higher protection against UVA rays than physical sunscreens.

Some sunscreens are a combination of both - with organic and inorganic elements in them. Both physical and chemical sunscreens can be applied the same way, and will work right away (it is a myth that you have to wait a few minutes for chemical sunscreen to work).

There is some controversy around organic sunscreens, which we will delve into in depth in another article. For now, I want to emphasise there is no compelling evidence that wearing organic sunscreens has any long-term adverse health effects. Some organic sunscreen ingredients have been shown to get absorbed into the skin and into the bloodstream, but in trace levels and not at any level known to have a physiological effect. The most important thing to remember is that this has not ever been shown to be at any meaningful level to cause harm. Chemical sunscreens have been used since the 1970s.

But do you know what an overwhelming amount of evidence shows will cause you long-term adverse health issues? Not wearing sunscreen. At the end of the day, I am not picky about what type of sunscreen you wear, as long as you wear it every day, and it is at an appropriate strength and broad-spectrum.

What does SPF actually mean?

SPF stands for "Sun Protection Factor." When sunscreens are tested in a lab, SPF is an indication for how long a sunscreen will protect you from UVB rays (and UVB rays only - not UVA!). A general rule of thumb is to multiply the number of minutes it normally takes you to burn by the SPF number. However, this is only referring to lab conditions, so you shouldn't actually think of SPF as an indication of how long your sunscreen will protect you.

Instead, think of SPF as an indication of how much more UV radiation your skin can be exposed to without burning.

A a minimum we should all be using SPF 30.

What do the stars on a sunscreen mean?

If SPF tells you about UVB rays, then the star system tells you about UVA rays. (Note that not all sunscreen use the star system.)

The number of stars a sunscreen is awarded indicates how broad-spectrum it is, ranging from 0-5 stars. At a minimum, you should be using a sunscreen of at least 4 stars if you're serious about protecting your skin.

So what are the most important factors to look for in sunscreen?

Make sure it is broad-spectrum, stating it covers both UVA and UVB, is rated at least 4 stars or higher and that is is at least SPF 30 or greater. Your skin will thank you!