Ultraviolet (UV) radiation is part of the electromagnetic spectrum and is found between visible light and X-rays.
The natural source is the sun.
Artificial sources include tanning beds; mercury vapour lamps; some halogen, fluorescent and incandescent lights; some lasers; and nail dryers, among others.
There are three types of UV radiation based on their wavelengths:
- Type A
UVA’s wavelength is 315-400nm and is not absorbed by the ozone layer.
About 90% of ozone is found in the stratosphere, which extends from about 10-15km to about 50km above the Earth’s atmosphere.
- Type B
UVB’s wavelength is 280-315nm.
It is mostly absorbed by the ozone layer, but some reaches Earth.
- Type C
UVC’s wavelength is 100-280nm and is completely absorbed by the ozone layer and atmosphere.
Almost all the sun’s UV radiation that reaches Earth is UVA, although some UVB radiation also penetrates through the ozone layer.
Both UVA and UVB radiation can affect health.
However, UVA penetrates deeper into the skin and is more constant throughout the year.
Ozone depletion, due to climate change, increases the UV levels on the Earth’s surface with effects on humans, animals and plants.
The intensity of natural UV radiation is dependent on latitude, altitude, cloud cover, time of day and ground reflection.
Health benefits and risks
UV radiation from the sun stimulates the human skin to produce vitamin D.
This vitamin is critical to human health as it facilitates the absorption of calcium and phosphorus in food, and assists in bone development.
Vitamin D deficiency leads to:
- Low blood calcium and phosphate levels
- Rickets in children, which causes softening bones
- Osteomalacia in adults, which leads to weak bones and bone pain
- Increased likelihood of type II diabetes, high blood pressure, autoimmune conditions and some cancers.
There are also potential associations with cardiovascular (heart) events, obesity and the metabolic syndrome.
While studies have reported various prevalence rates of vitamin D deficiency in Malaysians, the fact is that it is common despite Malaysia’s proximity to the Equator (which experiences equal and direct sunshine throughout the year).
ALSO READ: A paradoxical deficiency: Lack of vitamin D with all our sunshine
The risks of UV radiation are:
- Sunburn from short-term UV overexposure
- Premature ageing, wrinkles and skin cancer from prolonged UV exposure
UVA contributes to oxidative injury leading to loss of skin elasticity and wrinkles.
It also causes DNA (deoxyribonucleic acid) damage and oxidative injury, which increases the likelihood of skin cancers.
The commonest skin cancers are basal and squamous cell cancers, which usually involve the head, face, neck, hands and arms as these areas are the most exposed to UV radiation.
Most melanomas – the deadliest skin cancer – are due to UV radiation.
- Cataracts, photokeratitis and other blinding conditions from UV exposure
The World Health Organization (WHO) estimates that about 20% of cataracts may be caused or aggravated by UV exposure.
- Potential suppression of the body’s immunity due to UV overexposure, thereby affecting the body’s ability to fight infections.
The harms of UV radiation are increased in people:
- Who spend a lot of time in the sun or have sunburn from artificial sources
- Whose skin, eyes and hair are light coloured.
Although skin cancers are less common in the dark-skinned, it does occur and may be detected late.
- Are aged 50 years and above
- Who take some medicines like antibiotics, contraceptive pills, benzoyl peroxide products and some cosmetics, which may increase skin and eye sensitivity to UV in all skin types
- Who have a family history of skin cancer
- Who are children.
Protection
Protection against overexposure to UV radiation is multipronged and includes limiting exposure, wearing protective clothing, applying sunscreen and using sunglasses.
These measures include:
- Limiting sun exposure during peak UV hours, i.e. 10am to 4pm
- Avoiding tanning beds and sunlamps
- Monitoring the UV index daily to plan outdoor activities
- Seeking shade
- Using protective clothing rated with Ultraviolet Protection Factor (UPF), which provides consistent UV defence
Clothes with higher UPF values, e.g. 50+, block more UV radiation.
Tightly-woven, darker-coloured fabrics generally offer better protection.
- Using hats with wide brims (5-7cm) or shade caps to protect the face, ears and neck
- Using UV-blocking sunglasses that shield the eyes and surrounding skin
- Using broad spectrum sunscreen with SPF (sun protection factor) 15 or higher
It should be generously applied to all exposed areas, including the face, ears, neck, arms and tops of feet, 15 minutes before sun exposure.
It should be reapplied every two hours, or after swimming, sweating or towelling off.
Lip balm with SPF provides lip protection.
Sunscreen has to be combined with other protective measures.
- Protection of children because of their increased vulnerability.
UV index scale
The Ultraviolet Index (UVI) is an international standard that measures the intensity of UV radiation with respect to sunburn.
It was developed by Canadian scientists and adopted by the WHO and the World Meteorological Organization in 1994.
The objective is to help in effective protection from excessive UV radiation.
The UVI measures the intensity of UV radiation on a linear scale and is usually updated daily.
The values of the UVI range from zero upwards – the higher the UVI, the greater the potential for damage to the skin and eyes, and the less time it takes for harm to occur.
The WHO’s recommended sun protection according to UVI are:
- 0-2: You can safely enjoy being outside.
- 3-7: Seek shade during midday hours. Slip on a shirt, slop on sunscreen and slap on a hat!
- 8+: Avoid being outside during midday hours. Make sure you seek shade. Shirt, sunscreen and hat are a must!
The UVI for Malaysia can be found here.
Although UV radiation is vital for the body’s vitamin D production and has certain immune benefits, overexposure poses serious risks to our skin, eyes and overall health.
The balancing of safe sun exposure with protective measures is essential for everyone’s long-term well-being.
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email starhealth@thestar.com.my. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
