Understanding UV and SPF

Read our blog to understand more about UV and SPF.
Written by
Toby Nelson
Published on
May 12, 2023

What is ultraviolet light?

Ultraviolet (UV) light is actually a bit of a misleading name as we cannot see it with the human eye. The name comes from the discovery in 1801 when the German physicist Johann Wilhelm Ritter recorded invisible 'waves' of light that darkened silver chloride-soaked paper more quickly than violet light. "Ultraviolet" means "beyond violet"(from Latin ultra, "beyond"), as violet has the highest frequencies of visible light. Ultraviolet, therefore, has a higher frequency and therefore a shorter wavelength than violet light.

Ultraviolet light is better thought of as ultraviolet radiation, as light is a form of radiation emitted from the sun. 

Within the UV spectrum, there are two types of rays that can damage the DNA in your skin cells and lead to skin cancer. It’s important to protect your skin from both types:

UVB rays do not penetrate the skin surface very far, consequently, they primarily cause sunburn and play a significant role in the growth of skin cancer. A sunscreen’s SPF number refers mainly to the amount of UVB protection it provides.

UVA rays can pass deeper into the skin, therefore, leading to increased ageing of the skin. They can also cause sunburn   It’s important to look for the words “broad spectrum” on a product’s label, which means it has ingredients that can protect you from UVA as well as UVB rays.

It's important to protect yourself from excessive UV exposure since both UVA and UVB rays can damage the DNA in skin cells, leading to mutations and potentially causing skin cancer. Overexposure to UV light can also harm the eyes and contribute to eye conditions such as cataracts.

To minimise the risks associated with UV light, it's recommended to use sun protection measures such as wearing a broad-spectrum sunscreen, protective clothing (e.g.,hats, long sleeves), sunglasses with UV protection, and seeking shade when the sun is strongest (usually between 10 a.m. and 4 p.m.).


What Does the SPF Number Mean?

The SPF (Sun Protection Factor) number is a measure of the effectiveness of sunscreen products in protecting the skin from the sun's ultraviolet (UV) rays.It indicates how long a person can stay in the sun without getting sunburned compared to the time it would take without any sunscreen.

The SPF number primarily refers to the level of protection against UVB rays, which are responsible for sunburns and contribute to the development of skin cancer. The higher the SPF number, the greater the protection offered. Here's a breakdown of what the SPF number means:

1.     SPF 15: This is the minimum level of protection recommended by dermatologists. It blocks approximately 93% of UVB rays, allowing you to stay in the sun 15 times longer than if you weren't wearing any sunscreen.

2.     SPF 30: This offers higher protection, blocking around 97% of UVB rays. It allows you to stay in the sun 30 times longer without getting sunburned compared to not wearing any sunscreen.

3.     SPF 50: This provides even stronger protection, blocking about 98% of UVB rays. It allows you to stay in the sun 50 times longer without burning.

4.     SPF 50+ or higher: Sunscreens with SPF 50+ offer the highest level of protection available. They block about 99% of UVB rays and are recommended for people with fair or sensitive skin or those who are spending an extended period in direct sunlight.

It's important to note that the SPF number primarily indicates protection against UVB rays, but it doesn't necessarily reflect the level of protection against UVA rays. UVA rays contribute to skin ageing and can also cause skin cancer. To ensure broad-spectrum protection, it's recommended to use a sunscreen labelled as "broad-spectrum" that provides protection against both UVA and UVB rays.

It's also important to remember that sunscreen should be applied generously and reapplied every two hours or after swimming or sweating heavily, regardless of the SPF number. Additionally, sun protection should not rely solely on sunscreen; other measures like seeking shade, wearing protective clothing, and using sunglasses are also essential for comprehensive sun protection.

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