Sunburn and sun protection

Your susceptibility to sunburns is strongly dependent on your skin tone. Darker skin has more melanin than lighter skin, so Black people and people with darker skin are better protected from the sun than light-skinned Whites. But melanin isn’t immune to all UV rays, so there’s still risk for people with darker skin.

People with red hair, green eyes and freckled skin have the highest risk of contracting skin damage. The risk is also increased in spring, before getting used to the stronger light, and for travellers before getting accustomed to stronger sunlight at a destination.

General recommendations are often targeted at the typical population, whatever that means. If you descend from people who weren't that exposed to the sun, work indoors, or otherwise have increased risk of sunburn, don't be ashamed to be more cautious than these recommendations.

The risk of sunburn increases when the sun is high on the sky (see UV index below). It can also be increased by the intake of pharmaceutical products. Certain common antibiotics, contraceptives, tranquillizers, and malaria prophylaxis provoke over-sensitivity to sunshine.

Leaving the juice of lemons or other citrus fruit on your skin will increase the speed and intensity of skin damage. A little lime juice on your hand from making a couple of margaritas, followed by a quite ordinary day outdoors, can result in a severe "sunburn" (phytophotodermatitis) that can last for weeks and which will affect any sun-exposed part of your skin that the citrus juice touched. There are also some wild plants that give the same effect if you touch them.

The incidence and severity of sunburn has been increasing worldwide, especially in the southern hemisphere, because of damage to the ozone layer due to CFCs and because more people travel wider distances to different climate zones exposing skin accustomed to cold weather to heavy sunshine.

The UV index is an international standard that provides information about the intensity of the sun rays and, thereby, potential damage from sunlight on a particular day. The higher the value of the index, the higher the risk for sunburn.

Most weather websites now include a forecast UV value, and it's wise to look at the weather in advance of your trip to know what sun protection you will need.

But generally speaking, you can assess how likely you'll be affected by the sun by considering eight factors:

• Your skin (see Increased risks above)
• Latitude
• Season
• Time of day
• Altitude
• Weather
• Surroundings
• Ozone layer

• Latitude – strongest in tropics – specifically, the northern tropics from March 20th to September 23rd, and the southern tropics from September 23rd to March 20th
• Season – strongest in late spring and early summer, assuming no clouds. As the presence of spring rain showers mean that this period is quite cloudy in many areas, the peak can be locally pushed back to later in the summer.
• Time of day – strongest from 9AM to 3PM sun time, peaking at noon. Sun time is more or less reflected in the local time, but as the latter is a political matter it may be off by even some hours. Add one hour where daylight savings is observed (i.e. 10AM to 4PM). Adjust also for location in the time zone: the sun is early in the eastern edge (subtract half an hour if the zones are regular); later in the west (add half an hour).

These three factors can be combined into one easy measurement. The strongest rays are when the sun is above 45 degrees in the sky. In other words, your shadow is shorter than your actual height. Short shadows mean high UV intensity.

For the mathematically inclined, the general rules for the angle of the sun away from vertical at noon at latitude L are:

• L at the equinoxes, March 20 and September 23, anywhere.
• L-23° at the summer solstice for your hemisphere, June 21 in the Northern hemisphere and December 21 in the south.
• L+23° at the winter solstice, dates opposite to above.

The tropics are the region where that angle is sometimes zero, L ≤ 23° so L-23° ≤ 0 ≤ L+23°. Between the Tropic of Cancer (23°N) and Tropic of Capricorn (23°S), the sun is sometimes directly overhead.

Polar night occurs where L >= 67° so L+23° is sometimes greater than 90° and the midwinter sun is below the horizon even at noon. In summer, the sun is above the horizon even at midnight. Beyond the polar circles, where midnight sun occurs, the sun intensity is general so low that everyone but the most sensitive can be outdoors around the clock – but take care when there is snow, which will multiply the intensity by reflections, and at high altitudes. Also, the ozone layer is often thinner here in the spring, when sunshine and snow cooperate to burn your skin and eyes – and if you are from this side of the globe, your skin may not yet be adapted to the sun.

• Altitude – UV radiation increases rapidly with altitude.
• Weather – strongest on clear, dry days (but light clouds give no protection)
• Surroundings – sand, water, and snow reflect UV radiation into shaded areas, and this circumvents some UV protection, such as hats and umbrellas. And you get the reflected radiation in addition to normal sunlight.
• Ozone layer – the ozone layer in the atmosphere gives some protection against UV radiation, but its thickness varies. It is often thinner in the spring near the Arctic and Antarctic, which means more radiation than otherwise also in the temperate zones. These "holes" are not regular.

The sun emits more than one type of UV radiation. UV-C isn't a problem, as it doesn't make it through the Earth's atmosphere. UV-B is the one that causes what most people think of as sunburn. As its wavelength is short, UV-B only penetrates the uppermost layer of the skin (the epidermis) which therefore absorbs all of the UV-B energy and takes all the damage. Besides causing redness and pain, UV-B also directly damages the skin's DNA and is regarded as the most dangerous type of UV radiation. UV-A goes deeper into the skin and doesn't cause immediate and visible damage. Instead, it causes long-term skin damage.

When buying sunscreen, don't choose a version that just protects you from UV-B radiation. Exposure to either type of UV radiation increases the risk for skin cancer. Look for sunscreen that is labeled "full spectrum" or "broad spectrum", or that says that it blocks both UV-A and UV-B.

This is the day when the sun is strongest, and is sometimes called the first day of summer. It occurs on June 21st in the northern hemisphere, and December 21st in the southern hemisphere. Outside the tropics, it could bring the highest level of UV radiation of the entire year. Of course, the atmosphere hasn't had time to fully warm up to the peak of summer yet, and many places are still cloudy and cool. However, if it happens to be sunny, this is the time you need UV protection the most. On the first day of summer, the earth has completed shifting its axis by 23.5 degrees, and that brings tropical-like UV rays to the temperate zones.

• All locations in the tropics have the sun directly overhead at noon twice each year, and on an annual basis receive as much UV radiation as the equator does (assuming equal environmental factors).

• On the summer solstice, locations in the temperate zones (up to 47 degrees latitude) could receive more UV radiation than the equator. Virtually all of Italy, New Zealand, and the eastern United States is below 47 degrees. In the west, the U.S.-Canadian border is at 49 degrees.

• Locations between 47 degrees and the polar circle could receive as much UV radiation on the summer solstice as the tropics do on the other side of the equator (their winter). If it is a clear, sunny day on June 21st in Reykjavík, Iceland, it will have slightly more intense UV rays than Rio de Janeiro. This is due to Reykjavík being closer to the Tropic of Cancer (23.5 °N) than Rio.

Fortunately as summer progresses, the earth has re-shifted its axis more in line with the equator. The real danger is that a fair-skinned person who has not been exposed for months spends time out in the sun in the late spring or early summer unprotected. They may mistakenly think the UV radiation is not so bad yet, when in fact, it's even worse.

See also: Eye care

Sunglasses are a must in bright sunlight, and especially in areas where the surroundings reflect sunlight, such as beaches, glaciers, and deserts.

Make sure your sunglasses leave no gaps in the field of vision: If you gaze downward and can see past the sunglasses, your eyes will still be exposed to some UV radiation. In environments with high UV intensity, such as high altitudes, use ski goggles rather than sunglasses.

Though counter intuitive, clear or light tinted sunglasses offer better protection than dark tinted ones, since a) your natural aversion to sunlight is preserved, and b) your pupils remain constricted, letting less light into your eyes.

Clothing is by far the most effective defence against the sun, but not all clothing is UV resistant, and you can get burnt even while wearing some clothing.

When travelling in a tropical environment, wear a large hat or headscarf, a white or beige long sleeved shirt made of thick cotton, and a pair of long trousers. Avoid wearing shorts and T-shirts; use long-sleeved baggy clothing instead, which will keep you just as cool while avoiding sunburn. The back of your neck is especially prone to sunburn, so get a shirt with a collar and wear the collar upwards (or wear a cotton scarf). Also, protect your face and especially your forehead with a hat or a baseball cap. Wear shoes and socks when possible.

On the beach, don't take your clothing off except when swimming. Of course, in this case, don't stay in the water for long periods. Consider taking a UV-protective rash guard or sunshirt, and other clothing you can wear in the water. If you feel that staying fully clothed defies the whole point of beaches, wrap yourself in a thick sarong.

Consider traveling with a folding umbrella, which offers a large area of shade. The small ones can be smaller than a hat when collapsed. This is the most commonly used form of sun protection in parts of tropical Asia.

Do not spend extended time outdoors during the hours around noon without extensive sun protection, especially if you're traveling in the tropics. Use any shade available. If at all possible, plan outdoor activities such as swimming or boating in the early morning or late afternoon.

Applying sun protection lotions (sunscreen) is better than nothing, but bear in mind that even the best sun lotions only provide partial protection, and none are suitable alone for prolonged (2 hours or more) exposure to strong sunlight. Lotions are rated by SPF, sun protection factor, a measure of how much they reduce burning under artificial circumstances. Different countries have different standards for SPF labelling, but bigger numbers are generally better. There are two main types (chemical and mineral) and two main formats (lotion and aerosol spray), and they can be used interchangeably. For example, you might start your day with a thick layer of mineral lotion, and later spray a generous layer of chemical sunscreen on top of that. As of 2021, "natural" sunscreens usually perform worse than conventional sunscreens.

The effectiveness varies with how thickly the stuff is applied: More is better. The main problem with sunscreen is that people don't put enough on. Two adults should use up an entire bottle of sunscreen if they spend all day at the beach.

Sun lotions should be generously and repeatedly applied where clothing isn't possible or practicable, e.g., face, on the back of your hands, or on any exposed skin. The tops and bottoms of feet and back of knees can burn surprisingly fast. As thin clothing, such as an old T-shirt, provides only limited protection, it is a good idea to apply sunscreen under thin clothing as well.

To work effectively, preparations need to be reapplied every 2 hours or less. Most sunscreen washes off when it gets wet, so you need to apply it again when you get out of the water or if you perspire, even if it's been less than 2 hours since the last round. Water-resistant sun protection lotion can be applied if you are planning to stay in the water; it is normally effective for only 40 to 80 minutes.

Make sure whatever preparation you use is "fresh", as even the best formulas begin to lose effectiveness after more than a year. Make sure your sunscreen is allowed in your destination, as some destinations and resorts ban sunscreens that contain reef-harming compounds, such as oxybenzone.