How can light affect the skin?
American Institute of Physics

Skin is one of the body's major organs, acting as a protective boundary between the body and the rest of the world. The outside layer is called the epidermis, and the inside layer is the dermis, which contains nerve endings, sweat glands, capillaries, and hair follicles. It is the inner layer of the epidermis that is most affected by ultraviolet light, a major part of sunlight. This inner layer contains a type of cell called a melanocyte, which produces the pigment melanin -- the source of a suntan or sunburn.

Exposure to ultraviolet light causes the melanocytes in your skin to produce melanin, which absorbs ultraviolet light to protect the skin cells from sun damage. This is why we tan. Caucasian people have less pigment in their skin than some other races, and thus are more vulnerable to sunburn. A sunburn occurs when skin cells are damaged by ultraviolet light. The body responds by increasing bloodflow to the capillaries in the dermis layer of the skin to repair the damage, and this extra blood causes the redness of a sunburn. Melanocytes are also responsible for developing skin cancer, caused when the cells mutate after repeated exposure to ultraviolet light.

Surface reflections can increase the effects of ultraviolet exposure. For example, snow reflects 90 percent of ultraviolet light, which why is you can get a sunburn while skiing on a sunny day. Sand reflects as much as 20 percent of ultraviolet rays, perhaps one reason some people tan faster at the beach. Glass, however, absorbs ultraviolet light; this is why we don't get sunburned while driving or working in a glassed-in greenhouse.

Light therapy 'best for acne'
British Journal of Dermatology

Acne can cause great distress to sufferers

A blue and red light mixture seems to be most effective treatment for acne - reducing the number of spots by three-quarters, says research.
As many as one in 20 adults have persistent acne, which can prove stubbornly resistant to both over-the-counter creams and washes, and antibiotics.

Some acne does clear up significantly when exposed to UV light, but this is unsuitable as a long-term remedy because of the increased risk of skin cancer.

The new treatment, tested by doctors at Hammersmith Hospital in London, uses light, but removes the potentially damaging UV.

Instead, blue and red light wavelengths produced by a lightbox which the patient, all with moderate or mild acne, used for 15 minutes each day.

At the end of a 12 week period, these patients on average showed a 76% decrease in the number of visible spots on the area treated.

This was better than the other active treatments, although there were not enough patients to make this statistically significant.

And it was much better than simply treating with a box that produced only normal white light.

'Promotes healing'

Dr Tony Chu, who led the trial, claimed that the combination of lights both attacked bacteria contributing to the acne, and promoted healing in the skin.

He said: "Our challenge now lies in incorporating this treatment to more severe cases of acne and finding ways of incorporating this treatment into their therapy."

However, an expert from one of Europe's leading centres researching acne disputed whether the light could have an anti-bacterial quality.

Dr Richard Pojar, director of the Skin Research Unit at Leeds University, said that the state of mind of the acne sufferer could have a pronounced effect on the state of the disease.

He said: "There's no evidence that red or blue light has an anti-bacterial quality - these organisms are used to living in normal light, which has red and blue light in it."

He said that putting any acne sufferer on even a "placebo" treatment - which contains no active ingredient - tended to improve the acne, simply because the improved mental state tended to improve the levels of hormones in the body.

The research was reported in the British Journal of Dermatology.