The sun and skin appear to have quite a love-hate relationship. On the positive side of this relationship, sunlight has many beneficial effects on the skin, including killing skin surface bacteria, Vitamin D synthesis, providing warmth and UV radiation, which can be used in the treatment of certain skin diseases. On the flip side, excess exposure to the sun also poses risks to health, particularly to the skin. It can lead to heat stroke, acute sun burn, photo-allergic reactions, premature skin ageing, abnormal cell mutation of skin cells leading to skin cancer, and cause risk to eyes.

How much is healthy?

To understand this, a primer on sunlight first: The major components of sunlight are visible white infrared radiations and ultraviolet (UV) radiations. Among these, infrared spectrum mainly produces the heat effect, whereas the ultraviolet radiations penetrate the skin. UVA and UVB are the major components of UV radiation. UVC is the third, with the shortest wavelength. It gets largely absorbed by the ozone layer in the atmosphere so does not reach the skin.

Heatstroke: This is caused by the body overheating due to prolonged exposure to a hot and humid environment, and is usually called nonexertional (classic) heatstroke. The most common sufferers are outdoor workers. Similarly, strenuous physical activity in hot weather can increase the core body temperature, causing exertional sun stroke. The clinical signs and symptoms of an intense sun stroke include:

• High body temperature above 104F (40C)

• Headache

• Altered mental state or behaviour, for instance, confusion, agitation, slurred speech, and occasionally seizures; in extremely rare cases, a comatose condition

• Nausea and vomiting

• Flushed skin

• Rapid breathing

• Increased heart rate – the sufferer’s pulse rate can significantly increase because heat stress places a tremendous burden on the heart in an attempt to cool the body.

• In classic heatstroke, the sufferer’s skin will feel hot and dry to the touch whereas in exertional heatstroke, skin may feel dry and slightly moist.

A heatstroke victim should be promptly taken to a hospital for proper medical attention. Any unnecessary delay can be fatal.

How to avoid a sun stroke:

• Wear loose-fitting, lightweight clothing

• Use an umbrella or hat

• Drink plenty of fluids

• Never leave anyone in an outdoor parked car

• Get acclimatised – limit time spent working or exercising in heat until you’re conditioned to it.

• Be cautious if you are at increased risk – for example, people with cardiopulmonary disease need to take extra care

Sun-induced risks caused by UV radiation

The most common phototoxic reaction of the skin is sunburn. Susceptibility to get sunburn varies from one individual to another and within the same person from one skin site to another. Individuals of Caucasian origin with skin phototype I and II have the highest risk of sunburn.

UVB radiations are the major culprits in causing sunburn, as it is at its peak during midday hours.

Sunburn reactions could be mild, moderate or severe. Mild sunburn (Grade I) is seen with a short-lasting minimum degree of skin redness and usually is self-resolving. In moderate degree (Grade II) sunburn, the skin redness is more intense, causing burning sensations, mixed with severe itch. The affected area is tender to the touch.

In the severe form of sunburn (Grade III), affected skin areas are extremely inflamed and mildly swollen. In many cases skin develops vesicles, blisters and even bullous lesions (water-filled large-sized blisters).

Grade II and grade III sunburn reactions must be treated promptly by a qualified dermatologist. Grade II reactions are mostly treated with topical applications of steroids together with repeated use of skin emollients. In the treatment of grade III sunburn reactions, short courses of oral steroids are prescribed together with its topical applications. People of any age or gender can develop sunburn, but holidayers on sunny sandy beaches appear to be at a higher risk.

Skin photo-aging, however less hazardous for health, is the second most common concern connected to excessive sun exposure. In this case, UVA radiations are primarily responsible together with some UVB radiation. Many commonly used oral as well as topical medications can cause skin reactions on exposure to sun. In this case, they are labelled as photochemical skin reaction.

The most serious risk resulting from repeated prolonged sun exposure is skin cancer. UVB radiation in the sunlight is largely responsible for causing damage to the DNA of the cells, mainly in the epidermal layer of the skin. UVB is more intense from 10am to 4pm during peak summer months.

So, prolonged unprotected sun exposures must be avoided during these hours. The most common skin cancers caused by repeated excessive sun exposures are Basal Cell Carcinoma (BCC), Squamous Cell Carcinoma (SCC) and Malignant Melanoma (MM). BCC and SCC usually start with reddish blemishes on the skin, mainly of the exposed body areas, which later can become scaly papules or plaques and mostly can go unnoticed.

How to protect yourself:

• Avoid prolonged sun exposure between 10am and 4pm.

• Wear full body clothing made of closely knitted cotton fabrics.

• Wear a broad brimmed hat.

• SPF30-plus sunscreen should be applied on all the sun-exposed areas of the body. The first application should be at least half an hour prior to leaving your house and then subsequent applications must be done every two hours.

• For those indulging in water sports, sunscreen application guidelines become mandatory. Sunscreens with "water-resistant" slogans are still under debate. So, all sunscreens must be applied each time after coming out of water.

• Sitting under umbrellas in the beach or by the poolside offers only 25 per cent protection. They get 75 per cent of UV radiation reflected from surrounding sandy, stony or water surfaces.

• Golfers trying to finish a 18-hole game, which can take several hours, must wear dark UV blocking sunglasses in addition to the above-mentioned protective dressing guidelines. Wearing such sunglasses can significantly protect them from premature cataract formation.

What is SPF?

SPF stands for Sun Protection Factor and is a measure of a sunscreen’s ability to prevent UV radiations from damaging the skin. How it works: If it takes 20 minutes for your unprotected skin to start turning red, using a SPF30 sunscreen theoretically will prevent such reddening 30 times longer. However, for practical purposes this formula cannot be believed religiously.

What SPF is the best to use?

SPF 15 filters out approximately 90 per cent of incoming UVB rays. SPF 30 keeps out 95 per cent and SPF 50 about 98 per cent of the UVB rays. There is no sunscreen that is believed to block 100 per cent of UV radiation – therefore, the sunscreens labelled with SPF 50 onwards are not considered of any extra protection value.

Are there any total UV blocking sunscreens?

The majority of sunscreens available in the market are only capable of protecting you from UVB radiations in the sunlight. Exclusive UVA blocking sunscreens are not commonly available. However, sunscreens containing either zinc oxide, titanium dioxide, avobenzone, or oxybenzone can be considered with UVA blocking abilities. The sunscreens with UVA and UVB protection are usually labelled as Multi-spectrum, Broad Spectrum or UVA/UVB protecting sunscreens.

Who should use sunscreen?

Anyone over the age of six months should use sunscreen during sun exposure periods. Even those who work inside are exposed to ultraviolet radiation for brief periods throughout the day, particularly if they work near windows, which usually filter out UVB not UVA radiation.

Children under the age of six months should not excessively be exposed to the sun.

How much sunscreen should one use to get full SPF effect?

Apply one ounce of sunscreen (2 mg of sunscreen per square centimetre of the skin area).

Myths on sun exposure

Wearing sunscreen can cause Vitamin D deficiency: About 20 minutes sun exposure a day is enough for vitamin D synthesis. Vitamin D is also available in salmon, eggs, enriched milk, orange juice, if you tend to remain completely indoors.

You don’t need to use sunscreen on a cloudy day: Not true. Up to 40 per cent of the sun’s ultraviolet radiation reaches earth even on a completely cloudy day.

You don’t need to wear sunscreen in mountainous areas because it is too cold: Wrong. Temperatures during the day are influenced by infrared radiations of the sun and have no influence on UV radiation. As such, even in colder months one can get sunburn if you remain unprotected.

Dr Ikramullah Al Nasir is a dermatologist and medical director of Dermacare Centre.