UV Light: Positive & Negative Effects

Most ultraviolet (UV) light from the Sun is blocked by the atmosphere before making it to the surface, but the American Cancer Society points out that UV light is still the main cause of the damaging effects of sunlight on human skin. In most circumstances, you'll hear a lot more about the dangers of UV light than any positive effects it has; however, there are both advantages and disadvantages to those ultraviolet rays from the Sun. Learning about both sides of the issue – and what UV light actually is – helps you understand why most things you'll hear about it are negative.

UV light is very similar to visible light except it has more energy, and the wavelengths are too short to be picked up by human eyes. UV light is any electromagnetic radiation with a wavelength between 10 and 400 nanometers (i.e. 10 to 400 billionths of a meter), while the visible light range is between 400 and 700 nanometers. The shortest part of the visible range is violet light, so ultraviolet light is literally describing "beyond violet" light.

UV light itself is broken down further on the basis of wavelength. Light at the longer UV wavelengths of 315 to 400 nanometers is called UV-A light, while that at shorter wavelengths of 280 to 315 nanometers is called UV-B. However, almost no radiation under 290 nanometers actually makes it to the surface. Radiation at smaller wavelengths, between 100 and 280 nanometers, is called UV-C light. Extreme UV light occurs between 10 and 100 nanometers, but it can't get through the Earth's atmosphere.

A few positive ultraviolet light effects for humans are worth mentioning. The main one of these is the ability of UV light (specifically UV-A) to trigger the production of vitamin D by our bodies. This is needed for the bones, muscles and the immune system, and it is suspected to lower the risk of colon cancer.

UV light also has beneficial effects on skin conditions like psoriasis because it slows the growth of skin cells and thereby reduces symptoms. Sunlight exposure (i.e., UV exposure) also stimulates the production of tryptamines, which improve mood.

UV is useful for other purposes too, including disinfection and sterilization by killing bacteria and viruses. This happens because the high-energy rays can destroy DNA, so it's actually linked to a negative effect of UV, but this also means that bacteria and viruses can't reproduce or multiply. People exploit this effect in simple ways (such as hanging clothes outside to dry in the sunlight) and more technological ways (such as using UV lamps for antibacterial purposes).

Some insects and animals also depend on UV light. Some insects depend on UV radiation – mainly from objects in space rather than our Sun – for navigation. Other animals, including species of birds, bees and reptiles, see in near-UV light to help some flowers, fruits and seeds stand out more clearly.

There are several negative effects of UV light on humans. Increasing the risk of skin cancer is the most well-known of these, with about 90 percent of skin cancers being down to UV radiation (mainly UV-B, but UV-A rays are implicated too). UV rays also cause sunburn, damaging the skin cells and causing extra blood flow to the affected area, which leads to the reddened skin typical of sunburn.

The immune system is responsible for protecting the body from pathogens, and it's generally thought that UV radiation suppresses this system to some extent. The functioning and distribution of the white blood cells are affected up to a day after sunlight exposure, and excessive exposure may have even greater effects. UV light can also impact the tissues of your eye, effectively burning them and causing a condition called photokeratitis.

Finally, UV light is known to have some effects on animal life as well. One key impact of UV-B light is that it can impact the process of photosynthesis, reducing the size, productivity and quality of plants such as:

• corn
• cotton
• soybeans
• rice

It also has an impact on phytoplankton in the ocean (which produce energy through photosynthesis), reducing their productivity and having a range of knock-on effects for the ecosystem. UV-B is also thought to increase plants' susceptibility to disease.