Positive and negative effects of UV
The Earth’s atmosphere blocks most of the Sun’s UV radiation from penetrating through the atmosphere. The small amount that gets through has both positive and negative effects.
Researching UV and vitamin D links
Dr Richard McKenzie, Emeritus Researcher – Atmospheric Radiation at NIWA, Lauder, talks about the relationship between exposure to UV radiation and the body’s production of vitamin D.
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Positive (beneficial) effects of UV
Triggers vitamin D – UV from the Sun is needed by our bodies to produce vitamin D. Vitamin D helps strengthen bones, muscles and the body’s immune system. It may also lower the risk of getting some kinds of cancers such as colon cancer.
Helps some skin conditions – UV is used in the treatment of skin conditions such as psoriasis. This is a condition where the skin sheds its cells too quickly and develops itchy, scaly patches. Exposure to UV slows the growth of the skin cells and relieves the symptoms.
Helps moods – Research suggests that sunlight stimulates the pineal gland in the brain to produce certain chemicals called ‘tryptamines’. These chemicals improve our mood.
Helps some animals’ vision – Some animals (including birds, bees and reptiles) can see into the near UV light to locate many ripe fruits, flowers and seeds that stand out more strongly from the background. The fruits, flowers and seeds often appear quite different from how humans see them. For example, when seen in UV light, some flowers have different line markings, which may help direct bees and birds to the nectar.
Aids some insects’ navigation – Many insects use UV emissions from celestial objects as references for navigating in flight. This is why flying insects are sometimes attracted to artificial lights like lamps. It’s actually an example of their navigation process being disrupted!
Zapping bugs
Sanjay Kumarasingham (Watercare Services Ltd) talks about how microorganisms and viruses are zapped by UV radiation with a wavelength of 254 nm.
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Useful for disinfection and sterilisation – UV has positive applications for disinfection and sterilisation. UV can effectively ‘kill’ (deactivate or destroy) microorganisms such as viruses and bacteria, for example, when hanging cloth nappies, underwear and tea-towels outside on the clothesline. To destroy the microorganisms, UV rays penetrate the cell's membrane, destroying the DNA, and stopping its ability to reproduce and multiply. This destructive effect explains why we can use UV antibacterial lamps for disinfection and sterilisation. Mangere Wastewater Treatment Plant in Auckland use UVC light to disinfect wastewater.
Curing – UV light can be used to harden or ‘cure’ some glues, resins and inks by causing a photochemical reaction inside those substances. For example, dentists use UVA to set small fillings.
Negative (harmful) effects of UV
Causes skin cancer – UV is an environmental human carcinogen. It’s the most prominent and universal cancer-causing agent in our environment. There is very strong evidence that each of the three main types of skin cancer (basal cell carcinoma, squamous cell carcinoma and melanoma) is caused by sun exposure. Research shows that as many as 90% of skin cancers are due to UV radiation.
Moles and melanoma
Hayley Reynolds and Professor Rod Dunbar explain the changes in moles that can be signs of melanoma developing.
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Causes sunburn – UV burns the skin. Sunburn is a burn that occurs when skin cells are damaged. This damage to the skin is caused by the absorption of energy from UV rays. Extra blood flows to the damaged skin in an attempt to repair it, which is why your skin turns red when you are sunburnt.
Sunburned back
A sunburn, photographed two days after a five-hour exposure to the sun. The non-burned areas were covered by togs.
Damages the immune system – Over-exposure to UV radiation has a harmful suppressive effect on the immune system. Scientists believe that sunburn can change the distribution and function of disease-fighting white blood cells in humans for up to 24 hours after exposure to the sun. Repeated over-exposure to UV radiation can cause even more damage to the body's immune system. The immune system defends the body against bacteria, microbes, viruses, toxins and parasites (disease and infection).
Damages eyes – Prolonged exposure to UV or high intensities of UV (for example, in sunbeds) damages the tissues of the eyes and can cause a ‘burning’ of the eye surface, called ‘snow blindness’ or photokeratitis. The effects usually disappear within a couple of days, but may lead to further complications later in life. In 1998, the Journal of the American Medical Association reported that even low amounts of sunlight can increase the risk of developing eye damage such as cataracts, pinguecula and pterygium (also known as 'surfer’s eye'). UV damage to the eyes is cumulative, so it is never too late to start protecting the eyes.
Age of skin – UV speeds up the aging of skin, since the UV destroys collagen and connective tissue beneath the top layer of the skin. This causes wrinkles, brown ‘liver’ spots and loss of skin elasticity. The difference between skin tone, wrinkles, or pigmentation on the underside of a person's arm and the top side of the same arm illustrates the effects of sun exposure on skin. Usually, the top side of the arm has had more exposure to the sun and shows greater sun damage. Because photo-aging of the skin is cumulative, it is never too late for a person to start a sun protection programme. A tan may look good now, but you could be paying for it with wrinkly leathery skin or skin cancer later.
Cumulative sun damage
Two older men whose skin shows the effect of long term sun exposure.
The leathery wrinkles and yellow lumps are a form of damage called solar elastosis and it usually starts to present when people are in their forties.
Both images released under CC BY-NC-ND 4.0
Weakens plastics – Many polymers used in consumer items (including plastics, nylon and polystyrene) are broken down or lose strength due to exposure to UV light.
Fades colours – Many pigments (used for colouring food, cosmetics, fabric, plastic, paint, ink and other materials) and dyes absorb UV and change colour. Fabrics, furnishings and paintings need protection from UV fluorescent lamps as well as sunlight, to prevent colour change or loss.
Science is dynamic and changes
The role of science is to provide the best understanding of the world at the moment. This understanding is important so that we can best decide how to use this information.
Related content
You, Me and UV – introduction is a good article to start planning teaching and learning around UV. It includes links to multiple resources including:
Student activities
Use UV beads to help student learn about UV in: UV bead items, Investigating UV intensity, and Investigating sunscreens.
Students can investigate UV fluorescence in Rock fluorescence and Write a secret message.
Useful links
For more information UV exposure and health visit the Environmental Health Indicators New Zealand website.
Get to know your melanocytes, the cells responsible for producing melanin pigments that protect the body from the adverse effects of UV-B light exposure. This article is from Biology Online.
Science communicator Ed Yong explains the story of How Science Came To See Ultraviolet Light In Animals.
