Korean SPF Decoded: What the Numbers Really Mean

Posted by Skinsider Team on 1st May 2025

SPF Ratings, Broad Spectrum, and UVA vs. UVB Protection Explained

When it comes to sun protection, many of us focus on the SPF number alone but that’s only part of the story. Understanding SPF, PA ratings, and the difference between UVA and UVB rays can make all the difference in how well you protect your skin.

Let’s break it all down.

What Does SPF Stand For?

SPF stands for Sun Protection Factor. It measures how well a sunscreen protects you from UVB rays, the kind that cause sunburn and contribute to skin cancer. For example, SPF 50 means your skin is protected 50 times longer than if it were unprotected. SPF 50+ indicates protection that’s even higher than SPF 50 although not drastically more (around 98% vs. 98.5% UVB protection). While both offer strong protection, SPF 50+ gives just that extra bit of reassurance for those with sensitive skin or high sun exposure.

What About UVA Protection? (The PA System)

Here’s where it gets interesting. SPF only covers UVB rays, but UVA rays penetrate deeper into the skin and are responsible for premature aging, pigmentation, and long-term damage. That’s where PA comes in.

What Is PA?

PA stands for Protection Grade of UVA and was developed in Japan. It’s based on the Persistent Pigment Darkening (PPD) method, which evaluates how long it takes for UVA rays to cause skin darkening.

PA Rating System:

PA+ = Some UVA protection
PA++ = Moderate protection
PA+++ = High protection
PA++++ = Extremely high protection

The more pluses, the better the UVA protection. If your skin is prone to hyperpigmentation or you're concerned about aging, aim for PA++++.

UVA vs. UVB: What's the Difference?

UVB rays are the shorter wavelength rays that primarily cause sunburn. They're responsible for the immediate damage to the skin, such as redness, irritation, and peeling, and contribute significantly to skin cancer.
UVA rays, on the other hand, have a longer wavelength and penetrate deeper into the skin. They’re the primary cause of premature aging (wrinkles, fine lines) and hyperpigmentation (dark spots). They also contribute to the risk of skin cancer but cause more long-term damage rather than immediate sunburn.

SPF Before or After Moisturizer?

When applying sunscreen, the general rule is to apply it after your moisturizer, but before any makeup.

Moisturizer first: Apply your moisturizer as the first layer to hydrate and seal in moisture.
Sunscreen second: After your moisturizer has absorbed, apply your sunscreen as the final layer of your skincare routine to ensure it's effective at protecting you from UV rays.

This ensures that the sunscreen is not diluted or compromised by other skincare products.

Does Sunscreen Prevent Tanning?

Sunscreen does not completely prevent tanning, but it significantly reduces the likelihood of skin darkening. Here's why:

Sunscreens are designed to protect the skin from harmful UV rays, primarily UVB rays that are responsible for sunburn. However, the tanning process is largely caused by UVA rays, which penetrate deeper into the skin.
While sunscreens can help block both UVA and UVB rays (depending on the product), no sunscreen offers 100% protection. So, while it can greatly reduce tanning, it won’t completely stop it.

Even though sunscreen doesn't guarantee you won't get tan, it prevents the harmful effects of UV exposure such as premature aging and skin cancer, which are far more important in the long run.

Real-World Examples from Skinsider

Beauty of Joseon Relief Sun: Rice + Probiotics SPF50+ PA++++
A cult-favorite for a reason—this sunscreen provides broad-spectrum protection and a skin-loving formula with rice extract and probiotics. Ideal for dry or sensitive skin and those wanting the highest possible UVA protection.
LAGOM Cellus Sun Gel SPF50 PA+++
This lightweight gel is a hydration booster with solid sun protection. Great for combination or oily skin, offering a fresh, dewy finish without white cast.
COSRX Ultra Light Invisible Sunscreen SPF50 PA++++
Invisible, breathable, and intensely hydrating, this is a top pick for those who want high UVA/UVB protection without the heaviness.
Heimish Artless Glow Base SPF50+ PA+++
This multitasking product offers both sun protection and a radiant base for makeup. It’s your glow-boosting sunscreen-meets-primer.

Daily sunscreen use is the most effective anti-aging step you can take. Choose the right product for your skin type and protect your skin like a pro.