Ultraviolet (UV) light is electromagnetic radiation with wavelengths that are just shorter than visible light. Although humans can’t see UV light, many other animals can. UV light is most commonly found in sunlight and artificial UV sources, such as tanning beds and blacklights. UV light is classified into 3 general groups based on wavelength:
- UV-A (315-400 nm) – e.g. blacklights
- UV-B (285-315 nm) – e.g. tanning beds
- UV-C (100-285 nm) – e.g. germicidal UV light systems
UV Light and Skin
Sunlight contains a full spectrum of colors, including the UV spectrum. However, much of the shorter wavelength electromagnetic radiation in sunlight is absorbed by the atmosphere and does not reach the earth’s surface. As a result only low levels of UV-B, and minute levels of UV-C reach the earth’s surface. UV-B and UV-C light are both capable of causing damage to DNA and the collagen matrix that supports the skin. Because of this, excessive exposure to sunlight and/or tanning booths can accelerate aging of the skin and may increase the risk of skin cancer.
Exposure to ultraviolet light, particularly UV-B, can cause sunburns and trigger the production of the pigment melanin in a process commonly known as “tanning”. Exposure to UV light is important for the natural production of vitamin D in the skin. UV-B and UV-C light can directly damage DNA, which can cause genetic mutations. Strong UV-C light is toxic to bacteria and UV-C systems are commonly used to sterilize air or surfaces. Blacklights (UV-A) do not cause genetic mutations and do not pose a health risk.
UV Light, Sunlight, Tanning and Acne.
Exposure to UV light causes significant changes in the affected skin tissue, and these changes can impact acne symptoms. Many people strongly believe that tanning improves their complexion. While there is certainly some truth to this, the scientific research indicates that exposure to UV Light, tanning and sunburns are a mixed bag when it comes to acne.
Positive Effects of UV Light on Acne
- A tan (or a sunburn) can even out skin complexion, decreasing the appearance of acne.
- UV Light is toxic to the bacteria that cause acne, although it is unclear whether UV Light penetrates the skin deeply enough to have much benefit in this respect. Longer wavelength UV light (UV-A) can excite the porphyrins in Propionibacterium acnes bacteria, killing the bacteria in the same way as Blue Light Phototherapy.
- The increase in skin temperature during an acute sunburn may make sebum less viscous (less sticky), aiding in clearance of sebum plugs.
- Exposure to UV Light has been observed to modulate immune responses in the skin. One of these changes may be an inhibition or depletion of certain types of white blood cells called Mast Cells and Langerhans Cells, which are involved in immune activation and inflammation. Depletion of these cells could potentially result in short term improvements in acne by decreasing inflammatory responses in the skin.
Negative Effects of UV Light on Acne
- Some research studies have reported that UV Light can change some non-comedogenic molecules into comedogenic molecules, which may worsen acne symptoms for some individuals.
- Excessive exposure to UV Light can accelerate skin aging and increase the risk of skin cancer.
Overall, the research is inconclusive (and occasionally contradictory) regarding the relationship between UV Light exposure and acne. The specific effects of UV Light vary greatly between people with different skin tones. In addition the intensity and duration of the exposure to UV Light is very important. Our bodies have adapted over millions of years to respond to UV exposure by increasing melanin (skin pigment) production and upregulating many cellular DNA repair systems. Exposure to small doses of UV light can stimulate these processes, but large doses of UV Light (which cause significant sunburns) can overwhelm the body’s natural defenses and may cause permanent damage.
How and Where is UV Light Therapy Administered?
The most common source of UV light exposure is the sun. The second most common source are the UV bulbs used for tanning. Tanning beds usually employ fluorescent bulbs that emit UV-A and UV-B light. Ultraviolet light therapy is also administered in many dermatology clinics, primarily for the treatment of psoriasis and eczema. For these treatments, a specialized source of UV-B light (310-315 nm) is commonly used.
The cost of UV Light therapy varies from free (the sun) up to ~$100 per treatment (dermatologist). The cost of a tanning session (the most common source) often ranges between $5 and $25 per session. There are no established guidelines on the amount of exposure or treatment frequency for treating acne.
UV Light Images
Enhancement of comedogenic substances by ultraviolet radiation. Mills, et al. 2006.
Changes of comedonal cytokines and sebum secretion after UV irradiation in acne patients. Suh, et al. 2002.
Epidermal Langerhans Cell Depletion After Artificial Ultraviolet B Irradiation of Human Skin In Vivo: Apoptosis Versus Migration. Kolgen, et al. 2002.
Bivalent Effect of UV Light on Human Skin Mast Cells Low-Level Mediator Release at Baseline but Potent Suppression Upon Mast Cell Triggering. Guhl, et al. 2005.
Ultraviolet phototherapy and photochemotherapy of acne vulgaris. Mills, et al. 1978.
Pathophysiology of premature skin aging induced by ultraviolet light. Fisher, et al. 1997.
Photoinactivation of Propionibacterium acnes by near-ultraviolet light. Kjeldstad, et al. 1984.
A systematic review of the evidence for ‘myths and misconceptions’ in acne management: diet, face-washing and sunlight. Magin, et al. 2004.