Types of Ultraviolet Rays

In general, there are three types of ultraviolet rays:

1. UVA

UVA is a form of radiation that has a longer wavelength with stronger penetrating ability. Most UVA cannot be blocked by the ozone layer, and around 95% of the ultraviolet rays that usually reach the earth is UVA. While being able to darken the skin for a short time, it can also penetrate into the bottom layer of the skin and destroy cells in the dermis. UVA is also the cause of wrinkles and loss of skin elasticity. It may also trigger skin cancer.


2. UVB

UVB is a form of radiation that has a shorter wavelength with average penetrating ability. Most of UVB is blocked by the ozone layer, and around 5% of the ultraviolet rays is UVB. It can promote the formation of new melanin, make the skin darker for longer, and also thicken the epidermis. It should be noted that UVB will burn the skin and increase the risk of skin cancer.


3. UVC

UVC is a form of radiation that has the shortest wavelength that can be blocked by the ozone layer. Hence, ultraviolet rays in normal sunlight only contain UVA and UVB.

What Is the Sun Protection Index?

The sun protection measures we have to take are mainly products that can protect us from the damages caused by UVA and UVB. Now, let's learn about the meaning of sun protection index:

1. Sun Protection Factor (SPF) value: UVB Blocking Index

  • SPF 15: Blocks 94% of UVB
  • SPF 30: Blocks 97% of UVB
  • SPF 50: Blocks 98% of UVB

2. Value of PA = Protection Grade of UVA: UVA  Blocking Index

  • +: extends the sunburn-free time by 2~4 times
  • ++: extends the sunburn-free time by 4~8 times
  • +++: extends the sunburn-free time by 8 times or more
  • ++++: extends the sunburn-free time by 16 times or more

So does it mean that we have to choose sunscreen products with the highest SPF and PA values? 

Not really. Because sunscreen products usually lose their effectiveness two to three hours after application, we usually have to reapply them once every few hours. Therefore, applying sunscreen products with too high SPF will not bring much benefit. Rather, many users may take it too lightly and forget about the most important step of re-application.

Main Types of Sunscreen Products

There are two main categories of sunscreen products:

1. Physical sunscreens, such as:

  • Zinc Oxide
  • Titanium Dioxide


2. Chemical sunscreens, such as:

  • Oxybenzone
  • Octinoxate
  • Octisalate
  • Avobenzone

Although physical sunscreens are generally less likely to cause allergic reactions, the disadvantage is that most of them are oily, with some even look like putting white paint on the face. Hence, they are relatively less popular. In comparison, chemical sunscreens are more likely to cause allergic reactions. The advantage of chemical sunscreens is that they usually do not cause too much of a burden on the skin and are thus easier to be accepted by users. While both kinds of products have their own merits, the most important thing is to find a sunscreen product that can be used consistently. Click here to choose sunscreen products that are suitable for you.

Last Updated: Aug 2020
Please note that all medical health articles featured on our website have been reviewed by Quality Healthcare doctors. The articles are for general information only and are not medical opinions nor should the contents be used to replace the need for personal consultation with a qualified health professional on the reader’s medical condition.