Sunday September 30, 2007
Skin this!
By Dr TING HOON CHIN
Of summer, sunlight and skin cancers.
THOSE who live in colder climates usually look forward to summer. After the cold, dark winter, it is a relief to welcome summer, with its long warm days filled with sunlight.
In popular culture, summer is associated with beaches, vacations and traveling. In many countries, children are out of school during summer.
However summer is not all fun and frolic. There can be heat waves and forest fires that cause death and destruction. A more subtle danger that many people may not be aware of is the harmful effect of sunlight (specifically, the ultraviolet spectrum of sunlight) on the skin, which can lead to skin cancers, some of which may be fatal.
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The US National Institute of Health and the World Health Organization have both identified broad spectrum UV light as a human carcinogen. |
It is a scientific fact that UV radiation is the main causative factor for skin cancer. The US National Institute of Health and the World Health Organization have both identified broad spectrum UV light as a human carcinogen (something that initiates and promotes the development of cancer). UV light is responsible for over 90% of all skin cancers.
The ABCs of UV light
The solar UV spectrum is continuous but it is convenient to describe the light within three specific wavebands, UVA, UVB and UVC. They differ in their biological effects on the skin.
UVC is the shortest and highest energy UV, with a wavelength of less than 290 nm. However, since it is filtered out by the atmosphere and the ozone layer, these wavelengths do not reach the earth’s surface.
UVB is the middle range of UV, with wavelengths between 290-320 nm. It is responsible for sunburn, tanning and acceleration of skin ageing. It is also the most active spectrum in terms of skin cancer induction.
UVA is long wavelength (320-400nm) UV. It can penetrate into the deeper layers of the skin. It plays a major role in ageing and wrinkling. Recent studies indicate they may also initiate and exacerbate the development of skin cancer.
The visible light spectrum extends from 400-700 nm and infra-red, above 700nm.
These wavelengths are not known to induce skin cancers.
Types of skin cancer
The skin has several layers, but the two main layers are the epidermis (upper or outer layer) and the dermis (lower or inner layer). The epidermis is made up of three main cell types:
1. Squamous cells: thin flat cells that form the top layer of the epidermis.
2. Basal cells: round cells under the squamous cells.
3. Melanocytes: found in the lower part of the epidermis. They make melanin, the pigment that gives the skin its colour.
There are several types of cancer that start in the skin, but the two most common types arise from the basal and squamous cells and are called basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) respectively.
Melanoma is a cancer that arises from the melanocytes. It is a lot less common than BCC and SCC, but it is important because it is an aggressive cancer that often spreads and causes death.
Appearance, behaviour and causes of skin cancers
A BCC normally begins as a small, pearly, dome shaped lump on the skin and is often covered with small superficial blood vessels called telangiectasia. Some BCC contain melanin pigments, making them look blackish.
BCC can also present as a sore that bleeds, oozes or crusts and fails to heal. The edge of the sore is often raised and “thread-like”. BCC hardly ever spreads (metastasise) to other parts of the body. They can however cause a lot of damage by growing and invading surrounding tissue, especially if the site of the tumour is near the eye, nose and ear.
Acute episodes of intense burning sun exposure is more important than the cumulative life time sun exposure in causing the development of BCC
An SCC usually begins as a firm, indurated, skin-coloured or red lump on the skin.
SCC often starts on sun-damaged skin or traumatised scars. It is often capped by a hard crust that may be shed later to reveal an ulcer or eroded lump that bleeds rather easily.
SCC can sometimes spread or metastasise to other distant organs and cause death. SCC from the ear and lower lip are particularly prone to spread.
Cumulative and excessive total life time exposure to sunlight is the major cause of SCC. Occasional contributing factors are exposure to arsenic, presence of scars (especially burn scars), having chronic skin ulcers or inflammation and having a weakened immune system (especially in organ transplant patients on immunosuppressive drugs).
Melanoma usually presents as a changing pigmented patch or lump on the skin. It can arise in previously normal skin or it can arise in a mole. The following features aid in the diagnosis of melanoma.
The ABCDEs of melanoma
The features suggestive of melanoma are:
A = Asymmetry. If a line is drawn in the middle, the 2 halves are not equal.
B = Border. The border is irregular
C= Colour. Variation in colour is a warning sign.
D= Diameter. Melanomas are usually larger than 6mm (about the diameter of a pencil).
E= Evolving. Any change in size, shape, colour, thickness or any new symptom such as itch, altered sensation, oozing, bleeding or crusting is a danger sign.
If you observe one or more of the above features, go and see a doctor for further assessment. A biopsy will often be necessary to confirm or exclude the diagnosis.
Current evidence suggests that melanoma is in large part due to excessive sun exposure. The risk of developing melanoma is more related to intense intermittent exposure rather than continued, slowly cumulative occupational sun exposure over many years. Recreational sun exposure (e.g. related to sailing, swimming and sun bathing) is also an important risk factor. Blistering sunburn in early childhood increases risk.
The other risk factors of melanoma are:
1. Moles – the more moles you have, the greater the risk of melanoma. Individuals with three or more clinically atypical moles (dysplastic naevi) have a markedly increased risk of developing melanoma.
2. Family history. About 10% of melanoma patients have a family member with a history of melanoma.
3. Personal history. People who have or had BCC or SCC are at increased risk of developing melanoma. If you have had melanoma, you have an increased risk of recurrence.
4. Weakened immune system. Immune-suppressed people are at increased risk of melanoma.
Melanoma is an aggressive cancer and it is very important to detect it early. Survival rates for patients with early detection before it has spread is about 99% with treatment. But when it has spread, the survival rate drops to between 15% and 65%, depending on the extent of the spread.
How common is skin cancer?
Skin cancer is the most common of all cancers in many countries, accounting for about half of all cancers.
More than a million new skin cancers are diagnosed each year in the US and the rates are climbing. Most are BCC (about 800,000). SCC is less common (about 2000,000).
Melanoma is diagnosed in about 60,000 of people. Melanoma causes about 8,000 deaths a year and SCC about 2,200.
It has been estimated that one in five Americans will develop skin cancer in their lifetime.
The WHO estimates that worldwide, as many as 60,000 a year die from malignant skin cancers.
Skin types and skin cancer risk
Apart from sun exposure, your skin type is the main factor determining the risk of skin cancers.
There are six skin types, ranging in colour from type I (white) to type VI (black). In this country, the Chinese and Malays usually have type III and IV skin (yellow or light brown), while the Indians usually have type V (dark brown) or type VI (black) skin. This is of course a generalisation and there are individuals from each race who are much fairer.
Fair individuals with skin types I and II have the highest risk of skin cancer. People with type V and VI are at the lowest risk because those with more pigmentation have more natural protection from the sun. Individuals with skin types III and IV will have intermediate risk.
Despite the lower risk, people with darker skin can nonetheless get skin cancers and they should also protect themselves from the sun. In fact, melanomas are often more deadly in darker skinned people because it is more likely to develop undetected and be at an advanced stage when finally diagnosed.
Ozone layer and ozone depletion
Ozone is produced naturally in the upper part of the atmosphere (stratosphere) and it protects life on earth from the sun’s harmful UV rays.
This ozone layer is gradually being destroyed by man-made chemicals referred to as ozone depleting substances (ODS), including chlorofluorocarbon (CFCs), hydrochorofluorocarbon (HCFCs), methyl bromide, carbon tetrachloride, and methyl chloroform.
These substances were formerly used and still are used in coolants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants.
After release, the ODS slowly move into the stratosphere where they are broken down by the sun’s UV rays, and release chlorine and bromine molecules which destroy the ozone. It has been estimated that one chlorine atom can destroy 100,000 ozone molecules.
A slow steady decline of about 4% per decade in the earth’s stratosphere has occurred since 1980.
Ozone depletion can result in increased amounts of UV radiation reaching the Earth. As discussed earlier, overexposure to UV is recognised as the main cause of skin cancers. Thus it is possible that ozone depletion may be contributing to the rising incidence of skin cancers in the world.
How to protect yourself from the sun?
You should:
1. Seek the shade when appropriate, remembering the sun’s rays are strongest between 10am and 4pm.
2. Be extra careful near water, snow and sand as they reflect UV light and increase your chances of sunburn. Snow reflects 80% of light, sand 17%.
3. Use a sunscreen
4. wear protective clothing
5. Consider using UV protective films
How to choose and use your sunscreens
Choose a sunscreen with a sun protective factor (SPF) of at least 15 that provides wide spectrum protection against both UVB and UVA. The Environmental Working Group in US reviewed 780 name-brand sunscreens and found that one in eight did not protect against UVA.
Chemicals like PABA and PABA esters protect only against UVB. Look for the presence or addition of other ingredients like oxybenzone, avobenzone, parsol 1789, cinnamate, salicylate, mexoryl.SX , titanium dioxide and zinc oxide that extends protection to the UVA range.
Generously apply sunscreen to all exposed skin. An ounce (30 gram) is considered the amount needed to cover exposed areas adequately. Studies show most people apply only ½ to ¼ of that amount.
Sunscreens should be applied 15 to 30 minutes before going outdoors to allow the ingredients to fully bind to the skin. Reapply every two hours if you are in the sun for a long period.
Sun-protective clothing
Clothes can protect you from the sun’s harmful UV light. The tightness of the weave, the weight, type of fibre, colour and amount of skin covered all affect the extent of protection.
UPF stands for ultraviolet protection factor and indicates how much of the UV light is absorbed. A fabric with an UPF of 50, for example, will allow only 1/50 (i.e. 20%) of the UV light to pass through, thus giving good protection.
As a rule, light coloured, lightweight and loosely woven fabric do not provide adequate protection. A white, thin, cotton T-shirt provides only limited protection, with an average UPF of 7.
At the other end of the spectrum, a long sleeved, thick, dark denim shirt can offer an UPF of 1,700, which amounts to complete sun-block. Dark colours like black, blue or dark green gives better UPF than white. Unfortunately the favoured “summer clothes” are usually lightweight, light-coloured and skimpy.
High-tech clothing made from fabric specially treated with special UV absorbers are now available.
UV protective films
A car’s clear glass windows and windscreen filter out UVB light but not UVA light. Transparent UV filtering plastic films are available which screens out almost 100% of UVA and UVB without reducing visibility.
We should remember that the Road Transport Department in Malaysia requires cars to have at least 70% visible light penetration to the front windscreen and 50% for the rear windscreen and side windows. Thus we need to check the specifications of the films before installation to ensure that they meet this requirement.
UV protective films in bigger sheets are available for houses and offices as well. They block out up to 99.9% of UV light while allowing 30 to 80% of visible light to pass through, depending on the type of film.
A Shakespearian perspective?
William Shakespeare penned these memorable lines in Romeo and Juliet:
Give me my Romeo; and when he shall die
Take him and cut him out in little stars
And he will make the face of heaven so fine
That all the world will be in love with night
And pay no worship to the garish sun ...
Was the Bard a fortuitous pioneer in promoting sun avoidance?
The members of the panel include: Datuk Prof Dr Tan Hui Meng, consultant urologist; Dr Yap Piang Kian, consultant endocrinologist; Datuk Dr Azhari Rosman, consultant cardiologist; A/Prof Dr Philip Poi, consultant geriatrician; Dr Hew Fen Lee, consultant endocrinologist; Prof Dr Low Wah Yun, psychologist; Datuk Dr Nor Ashikin Mokhtar, consultant obstetrician and gynaecologist; Dr Lee Moon Keen, consultant neurologist; Dr Ting Hoon Chin, consultant dermatologist; Assoc Prof Khoo Ee Ming, primary care physician; Dr Ng Soo Chin, consultant haematologist. For more information, e-mail starhealth@thestar.com.my The Star Health & Ageing Advisory Panel provides this information 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 Health & Ageing Advisory Panel disclaims any and all liability for injury or other damages that could result from use of the information obtained from this article.
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