Sunlight is composed of
- 66% of infra-red light (it emits heat)
- 32% visible light (the light that allows us to see different colours)
- 2% ultraviolet light (UVL).
UVL is subdivided into:
- Ultraviolet A (UVA wavelength 320-400nm)
- Ultraviolet light B (UVB) which is a shorter wavelength (290-320nm)
- UVC( 260-290nm).
Why do we need protection from the sun?
UVB is the main cause of sunburn, and UVA can augment or add to the effects of UVB on the skin. UVC is the most dangerous – however UVC is filtered by the ozone layer in the atmosphere. This ozone layer is decreasing due to atmospheric pollution and hence the amount of UVC filtering through the atmosphere is increasing. This has lead to concerns about the increasing incidence of skin cancer.
To understand why different people get different responses to sunlight. we need to understand about skin types
Pigmentation/Photo ageing :
Both UVA & UVB are responsible for pigmentation. Pigmentation of skin along with wrinkling
Is one of the first signs of photo ageing (primarily caused by UVA ). So as a preventive measure, dermatologists recommend the use of sunscreen everyday.
UVA + UVB Sun Danger: Features of UV Rays
|‘B’ for burning (sunburns)||‘A’ for ageing (visual wrinkling, pigmentation disorders and sun spots)|
|2% of all sun light||98% of all sun light|
|penetrates less||penetrates less deep|
|Pigmentation – delayed tanning Causes increase in melanin||Pigmentation in hours responsible for immediate tanning commonest cause of allergic reactions|
|Produces DNA mutations leading to skin cancers||Penetrates deeper / present throughout the year|
|Intensity of UVB is highest during Midday||Penetrates window glass and cloud cover (exposure possible during indoors & driving)|
Immediate tanning is caused by UVA. Whereas UVB is responsible for delayed tanning. Tanning is a natural defence of the skin but is not effective against excessive exposure. Avoid tanning lotions. Sun bathing must be reduced.
Skin types and skin reactivity
People are divided into different skin types based on the amount of melanin (the pigment that gives us our skin colour) content in our skin, and on the capacity of our skin to darken or tan in response to sunlight. The following is one type of classification
- Type-1 Always burn, never tan
- Type-2 Usually burn, tan with difficulty
- Type-3 Sometimes burn, sometimes tan
- Type-4 Burn minimally, always tan
- Type-5 Rarely burn, tan profusely
- Type-6 Never burn, deeply tanned
People with skin types I (like the Irish) and II (some Caucasians), will tend to have a higher risk for the development of skin changes caused by sunlight exposure. Most south Indians are of types 3-5. Melanin pigment present in our skin absorbs the harmful UV rays and protects us from skin cancer.
What is sunburn?
This is an acute response of the skin to excessive UVL exposure and manifests as redness. It may be associated with pain and swelling. Sunburn is mainly caused by the UVB component. It begins several hours after exposure, and reaches a peak after 12-24 hours. Longer exposures cause a more rapid and persistent response. The redness (burn) fades over several days to be followed by skin peeling and tanning.
UVL in the sun causes tanning in 2 phases viz immediate pigment darkening (IPD) and delayed tanning (DT). IPD is a rapid darkening which begins soon after UVL exposure and is maximal immediately afterwards. It is due to UVA. It fades within a few minutes if the intensity of the exposure is small. DT is induced by UVB and occurs about 3 days after sun exposure
Changes in skin thickness
Exposure to the sun causes thickening of the outer layer of the skin.
Repeated exposures to sunlight will, in the long term, cause photo ageing to the skin. The skin becomes coarse, rough. wrinkled, leathery with uneven pigmentation and easy bruising. Skin with severe photo ageing tends to develop skin cancers. Most of these skin cancers can be easily removed by surgery, but sometimes they can erode deep into the tissues or spread to other organs. However skin cancer is very rare in Indians because of the presence of melanin which acts as natural sunscreen.
Abnormal skin reactions to sunlight
There are certain skin and medical conditions that are made worse or aggravated by sunlight. These include a common condition called melasma – which causes black pigmentation on cheeks in women. These patients should use sunscreens and avoid sunlight. Sunlight can also on its own, cause certain abnormal skin reactions. These are called photo dermatoses. Some of these are of unknown cause and can occur in any age group. An example is the polymorphous light eruption which is quite common in Europe and the United States. Some abnormal skin reaction to sunlight is due to contact with certain chemicals or due to the ingestion of certain medications. Examples are contact with musk ambrette, a synthetic perfume used in male colognes, or ingestion of certain antibiotics or anti-diabetic medications. Avoidance of the offending agent usually clears the condition.
Role of Sun protection
It is important to avoid excessive sun exposure. The sun’s rays are strongest between the hours of 10am to 3pm. Clothing also has some bearing on the effects of sun exposure. Cotton fabrics provide superior protection from sunlight and tightly woven fabrics afford better protection than loose weaves.
In addition to this, the routine use of sunscreen is an important part of basic skin maintenance. There are basically two types of sunscreens:-
- Physical sunscreens contain opaque, physical barriers such as titanium dioxide and zinc oxide which reflect the light energy,
- Chemical sunscreens, which contain chemical ingredients such as paramino-benzoic acid, avobenzone, to absorb the ultraviolet rays.
The SPF (Sun Protection Factor) indicates the degree of protection the sunscreen offers. Generally an SPF of 20 or more is advised. Always opt for a sunscreen which absorbs both UVA and UVB. As a guide most sunscreens should be applied at least twenty to thirty minutes before going out. You should re-apply after prolonged swimming or excessive perspiration.
Apply the sun care product 20-30 minutes before moving outdoors, repeat application should be necessary after every 2 hours.
50%-80% of the rays break through the cloud. Hence, even on a cloudy day, sun care products must be applied regularly.
No exposure to sun for children below 3 years of age – over 3 years of age protect children using a maximum sunscreen without forgetting a hat, t-shirt and sun glasses.
Monitor your moles or nerves (for cancerous changes) regularly for asymmetry, irregular edges, uneven colour and increase in size. In the event of any suspicion, please contact your dermatologist.
In spite of high SPF, certain products hardly provide any protection against UVA. So, choose a sun care product that is as effective against UVA rays as against UVB rays. UVS index is the protection against photo ageing and immediate pigmentation. UVA 16 increases 16 times the natural resistance of the skin against UVA.
Certain products do not resist water or sand friction. The protective filter is altered and Uvs can reach the skin. Look for the mention “water and sand resistant” above all “for children” products. Water resistant sunscreens protect the skin for 40-60 minutes of water exposure.
Check the texture and opt according to your requirements for a fluid, gel, cream or milk. Prefer sunscreens which spread easily without leaving shite marks. Look for the mention “non-comedogenic and hypo-allergenic”