What's the Difference Between UVA and UVB Rays?

Medically Reviewed by Stephanie S. Gardner, MD on July 24, 2023
Written by WebMD Editorial Contributors
4 min read

‌UVA and UVB Rays are different types of a form of energy called ultraviolet (UV) radiation commonly seen as sunlight. Both UVA and UVB rays can cause harm to the skin. But there are some health benefits available from UVA and UVB rays. Making sure you protect your skin can help you lessen the risks of harmful exposure to both types of rays. 

‌UVA and UVB rays differ from each other by how strong their energy is. They also differ from each other by how deeply they enter the different layers of your skin. Your skin has three layers,  an outermost layer called the epidermis, a middle layer called the dermis, and a layer right at the bottom called the subcutaneous fat layer.

Last but not least, scientists use a term called ‘wavelength’, a measure of distance, to show the differences between both types of rays.

‌UVA rays have a lower amount of energy and a longer wavelength than UVB rays. They can enter the middle layer of your skin called the dermis. UVA rays form 95% of the UV radiation which reaches the earth. They have a role to play in the formation of some types of skin cancers.

‌UVB rays have slightly more energy than UVA rays. They have a short wavelength that can only reach the outer layer of your skin called the epidermis.  UVB rays have been linked to skin burning. They also have an important role in the formation of skin cancers, especially a dangerous form of skin cancer called malignant melanoma.

‌UVA and UVB rays can affect your skin differently, but both can cause serious harm. UV radiation, in general, can also cause damage to your eyes and weaken your immune system. 

The following are risks associated with UVA exposure: 

Premature skin aging. UVA rays have been linked to skin aging because they penetrate the skin on a deep level. A common sign of early aging caused by UVA rays is wrinkle formation, also called photoaging. 

Skin tanning and skin cancer. UVA rays can cause your skin to tan. Tanning is your body’s way of protecting your skin from the damage caused by exposure to UVA rays. Getting a tan is not safe or healthy because UVA rays have been linked to the formation of skin cancers. 

It’s important to find ways to protect your skin from exposure to UVA rays. Always look for the words ‘broad-spectrum’ on your sunscreen label for a sunscreen that protects you from UVA and UVB rays. ‌UVA rays can go right through glass and clouds. A UV window film is one method you can use to block UVA rays from entering the windows in your home or your car. 

The following are risks associated with UVB exposure:

‌ Skin damage. UVB rays enter the upper layer of your skin and can cause damage in the form of sunburns and tanning. 

Skin blistering. UVB rays can cause a serious condition called blistering. A blister is a skin condition where fluid fills up space between different layers of skin. Blisters can be painful.

Skin cancers: Exposing yourself to UVB rays can increase your risk of getting skin cancer especially basal cell carcinoma, and squamous cell carcinoma. It can also cause a serious type of skin cancer called melanoma. 

As with UVA rays, it’s important to take steps to protect yourself from the harmful effects of UVB rays. Sunscreens usually offer protection against UVB rays. UVB rays are not able to go through glass. 

‌UVA and UVB rays do have some health benefits. ‌UVB rays can help the skin make vitamin D3 which is important for muscle and bone health. 

UVB and UVA rays are both used in a form of light therapy called phototherapy. Phototherapy can benefit serious cases of:

Rickets. A condition seen in children where the bones get softer and weaker because of a lack of vitamin D. 

‌Psoriasis, eczema. Skin conditions where your skin can turn red, scaly, or itchy. 

Vitiligo. A condition where patches of your skin lose color 

Phototherapy has also shown possible benefits for pain relief and:

Localized scleroderma. Also called Morphea, localized scleroderma is a rare condition that causes your skin to have reddish patches of thick or hard skin.

‌While UVA and UVB rays can cause serious and life-threatening medical conditions, you can minimize the risks by taking steps to protect yourself:

  • ‌Always wear sunscreen with a zinc oxide concentration of at least 8% and a minimum SPF of 30.
  • ‌Wear sun-protective clothing like long sleeved-clothing, sunglasses, and hats.
  • ‌Use a UV window film for your windows. 
  • ‌Stay out of the sun as much as possible during the hottest time of the day, which is from 10:00 am to 4:00 pm.