UVA rays have a longer wavelength than UVB rays. This length difference can influence the effect that exposure has on the body. For example, UVA is linked to the aging of skin, while UVB can cause sunburns.
UVA rays comprise 95 percent of the UV radiation reaching the surface of the Earth.
What Is UV Radiation?
Ultraviolet (UV) light is electromagnetic radiation with a wavelength of 10 to 400 nanometers (nm). This length is shorter than light, so it is not visible to the naked eye. However, it is longer than x-rays.
UV radiation derives from the sun and some man-made objects, such as tanning beds. Radiation simply refers to the energy that is emitted from a source, and it can range from very low to very high levels of energy.
UV radiation exists approximately in the middle of the spectrum of energy. For comparison, x-rays and radio waves emit very low levels of energy. Intuitively, higher levels of energy have more potential to cause damage to the human organism.
What Is the Difference Between UVA & UVB?
UV rays differ in their wavelengths and levels of energy.
UVA rays have longer wavelengths and energy levels, ranging from 315 to 399 nm. This type of radiation can result in damage to the skin over time, such as that associated with aging.
UVB rays have slightly more energy and can cause damage to DNA within the skin cells, such as via sunburns. UVB rays are also more likely to cause skin cancer than UVA rays. These rays have wavelengths of 280 to 314 nm.
A third group of UV rays exists as well, known as UVC rays. These rays have the highest level of energy of the three. They react with ozone in the Earth’s atmosphere and do not reach humans on the ground.
UV Ray Index
The UV ray index (UVI) is a measure of the level of UV radiation in the environment at any given time. The level of UV radiation can change based on several factors, such as sunlight, changes in stratospheric ozone, and climate change over time.
UVI can help provide an indication of the level of risk to harmful levels of radiation at any given time. It is based on the following scale:
- 0–2: Low (Green)
It is safe to be outside using normal sun protection. SPF 30 is recommended as well as sunscreen that contains zinc.
- 3–5: Moderate (Yellow)
It is advised to remain in the shade once late morning arrives through mid-afternoon. Sunscreen with an SPF of 30 or more is recommended as well as a hat and sunglasses.
- 6–7: High (Orange)
It is best to remain in the shade throughout the day and protect the face and any other sun-exposed skin by wearing SPF 30+ sunscreen and long clothing.
- 8–10: Very High (Red)
Complete avoidance of any sun exposure during the day is recommended. If going outside, cover as much of your skin as possible and apply SPF 30+ sunscreen.
- 11+: Extreme (Purple)
The skin and eyes can burn in just minutes at this level. It is best to avoid sun exposure completely.
Precautions to Take
This is a summary of the precautions that should be taken at each level of UV exposure:
|Amount of Risk
|Amount of Time It Takes to Burn
|Precautions to Take
|Sunscreen and protective eyewear
|SPF 30+ sunscreen and protective eyewear
|SPF 30+ sunscreen and protective eyewear, brimmed hat
|SPF 30+ sunscreen and protective eyewear, brimmed hat, long sleeves and pants, umbrella
|SPF 30+ sunscreen and protective eyewear, brimmed hat, long sleeves and pants, umbrella, avoid sun at midday
Risks of Exposure
The following risks exist with UV exposure (note that higher or more prolonged exposure increases the level of each risk):
- Skin aging
- Skin cancer
- Blindness and eye disease
Exposure to sunlight can have positive effects, such as increasing the production of vitamin D. However, you do not need much, so it is best to take precautions whenever you are planning to be outdoors.
Radiation: Ultraviolet (UV) Radiation. (March 2016). World Health Organization.
UV Index Overview. (October 2022). United States Environmental Protection Agency.
UV Radiation. (July 2022). Centers for Disease Control and Prevention.
Comparison of the Biological Impact of UVA and UVB Upon the Skin With Functional Proteomics and Immunohistochemistry. (November 2019). Antioxidants.
Update on UVA and UVB Radiation Generated by the Sun and Artificial Lamps and Their Effects on Skin. (February 2015). International Journal of Cosmetic Science.
UVA Radiation, DNA Damage, and Melanoma. (September 2022). ACS Omega.
Last Updated January 21, 2023
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