UVA vs UVB radiation: What's the difference?

The sun emits ultraviolet (UV) radiation, which consists of different types of rays including UVA and UVB. These affect your skin in different ways. Let’s look at the differences between UVA and UVB rays, and how you can protect your skin from harm.

UV radiation

UV radiation is an electromagnetic energy that most commonly comes from the sun, lasers, black lights and tanning beds. UV rays are classified according to their wavelength: UVA (longest wavelength), UVB (medium wavelength), and UVC (shortest wavelength). UVC rays are filtered out by Earth’s ozone layer which means they never reach the ground.

UVA rays = skin ageing

Ultraviolet A (UVA) rays are more penetrating than UVB rays, so they affect deeper skin cells. These rays cause indirect damage to cells’ DNA which leads to premature skin ageing such as wrinkles, lines and sagging.

About 95 per cent of the sun's UV radiation that reaches the ground are UVA rays. They cause an immediate tanning effect (the result of your skin cells trying to protect themselves from further harm) and sometimes sunburn.

UVA rays are the main type of radiation used in tanning beds, and can easily penetrate windows and clouds, which is why you can still get sunburnt on a cloudy day!

UVB rays = sunburn and skin cancer

Ultraviolet B (UVB) rays damage the outermost layers of the skin, directly damaging the cells’ DNA and causing most skin cancers. They can also cause premature skin ageing.

Even though only five per cent of UV rays that reach the ground are UVB rays, exposure to this form of radiation can cause sunburn in as little as 10 minutes. Symptoms of sunburn usually appear within a few hours.

UVB rays don’t penetrate windows and are more likely to be filtered out by clouds.

When are UV rays strongest?

UV radiation is strongest (and therefore more likely to damage your skin) between 10am and 4pm because the sun is at its closest point to Earth during this time. UV levels peak in spring and summer (when the sun is at a higher angle) but can still affect your skin in cooler months.

The temperature doesn’t impact the strength of the sun’s UV rays, which can’t be seen or felt.

UV rays are strongest at higher elevations (such as on an plane or mountain) and at the equator. Clouds filter out only some UV radiation, so you can still be sunburnt on a cloudy day. UV is also more intense when reflected by surfaces like snow, water, sand, glass or concrete.

How to protect yourself

Adopting sun-safe habits will protect you from both UVA and UVB radiation. Apply sunscreen every day, wear a hat and sunglasses whenever you go outside, avoid the outdoors during peak UV times, and get a regular skin cancer check to catch any suspicious lesions at their earliest stage when chances of treatment are best. You can check UV levels every day via your weather forecast.

It’s important to choose a broad-spectrum SPF50+ sunscreen. Broad-spectrum means it will protect against both UVA and UVB rays.

Written by National Skin Cancer Centres