In Victorian times, women quite sensibly shunned the sun and valued porcelain-white skin. Noel Coward alluding to the harmful effects of sunlight remarked that "Mad dogs and Englishmen go out into the mid-day sun". So common sense seemed to have prevailed during earlier times. Nowadays, however, people talk of the "great tan" or a "healthy tan". Well, the truth is there is nothing great about a tan which medically, represents sun-damage and accelerates skin ageing and increases the risk of skin cancers developing. Sun-damage takes place slowly and insidiously and the signs do often do not appear until 10 - 20 years later, lulling people into complacency. The depletion of the ozone layer has increased the amount of sunlight reaching the earth's surface and this is thought to be partly responsible for the increase in the incidence of skin cancers. I always tell patients that if they want to see the effects of the sun on the skin just look at the difference between the skin on the inside of the upper arm (the buttocks would be a better place but its not so convenient!) and the exposed skin on the outer part of the forearm. I then tell them this is only the cosmetic consequence but there is also the medical consequence which is the development of skin cancers. My patients seem to take better notice then.

SOLAR RADIATION

The figure below shows the different types of radiation (ultraviolet rays) emitted by the sun. Only the portion known as the terrestrial solar spectrum reaches the earth's surface. The earth's ozone layer absorbs ultraviolet (UV) rays below 330nm and almost all rays below 295nm. In other words, visible light (the colours of the rainbow  with a wavelength of 400 - 700nm), some UV-A (320 - 400nm), UV-B (290 - 320nm) and no UV-C (200 - 290nm) reaches the earth’s surface. More UV-B and UV-A rays are reaching the earth now because of the depletion of the ozone layer and this is one of the possible reasons for the increase in the number of cases of skin cancers. Depletion of the ozone layer has resulted in a large hole over the Antarctic and this is believed to have been caused primarily by the use of chlorofluorocarbons (CFCs), hence the move to ban their use.

	200nm	290nm	320nm	400nm	700nm
Gamma rays	X-Rays	Ultraviolet (UV)			Visible Light	Infra Red
		C	B	A
			Sunburn, Skin cancer, Ageing	Tanning, Skin cancer, Ageing

UV-B are short wavelength rays that penetrate the top layer of the skin and cause sunburn. In the past, it was thought that one could protect the skin against sun-damage by merely screening out UV-B. This was a mistaken view. UV-A takes longer to produce a burn but penetrates more deeply into the dermis and is now thought to be mainly responsible for the damage to collagen and elastin fibres that keep the skin firm and elastic. UV-B is thought to be responsible for causing sunburn, basal cell and squamous cell cancers. UV-A causes tanning and acts with UV-B to promote the development of skin cancers, including malignant melanoma. Being of a longer wavelength, UV-A can also penetrate the ozone layer better than UVB and can penetrate glass which UV-B cannot. The amount of UV-B varies, being maximum from 10am - 2pm (11 - 3pm during daylight saving hours) whereas the amount of UV-A is virtually constant. This means that we are actually exposed to more UV-A than UV-B on a day to day basis, inside buildings and in the car. So always protect the exposed skin with sunscreens effective against UV-A as well as UV-B.

Another surprising observation is that even incidental exposure to the sun is harmful. Dr Nicholas Lowe and his colleagues in the US irradiated the backs of volunteers with UV rays of a dose that was equivalent to what most of us get by walking to and from the car and driving a car. After 3 months, they found changes in the melanocytes, the blood vessels in the skin and also the elastin fibres that indicate sun-damage.

SKIN PHOTOTYPES

The degree of protection our skin has against the sun is directly related to the amount of melanin pigment in the skin.

The Fitzpatrick skin phototype classification is also useful for determining suitability for resurfacing treatments such as chemical peels, dermabrasion and laser resurfacing. Phototypes I - II are good for all these treatments but darker skin types, especially phototypes III and IV are more prone to develop temporary post-inflammatory hyperpigmentation (increased pigmentation compared to the surrounding skin. Forget about using the skin phototype as a guide to determine the SPF of a sunscreen to use so as to get a tan because tanned skin is simply sun-damaged skin. There is no such thing as a healthy tan!

SIGNS OF SUN-DAMAGE

Sun-damage occurs insidiously over the years until all of a sudden, you may realise that you have suddenly aged. Because of the long incubation period, people participating in outdoor sports without adequate sun-protection and sun-tanning in order to get the “healthy tan” won’t realise the damage until 10 - 20 years later. You may remember the weather-beaten face of the man in the old Marlborough advertisement. He may appear rugged to some but medically, he has severe photoageing, looks much older than he is and is at increased risk of developing skin cancer. If you want to see how much of the changes are due to photoageing just look your buttocks (in the privacy of your home) which is shaded from the sun and hence, represents chronological ageing and compare it with the backs of your forearm or the tops of your hands which are exposed to the sun. Just imagine, if you had taken precautions against the sun, your skin would look more like your buttock skin. See how much better it is!

“Just how bad is my skin in terms of photoageing”, you might ask. Doctors use a 4 grade classification and it simple enough for you to use. The grading system is a good guide for gauging the response to treatment, as well. As a general guide, cosmetic procedures for ageing skin will improve matters by only a grade, i.e., from Type III photoageing to Type II, so don’t expect miracles. It also means that, if you seek treatment early, when photoageing is just grade I or II, you are more likely to look better.

Classification of photoageing

(Modified from Glogan R G: Chemical Peel Symposium. Amer Acad Dermatol Atlanta, Dec 4, 1990):

Asians and other races with skin phototypes IV and above have more melanin pigment shield the dermis (deeper skin) and protect them from wrinkles. However, their melanocytes bear the brunt of the damage from UV rays leading to melasma, age spots (solar lentigines) and idiopathic guttate hypomelanosis (reverse of age spots) and unevenness of pigment tone. Wrinkles seem to occur at a later age than their caucasian counterparts.