Overexposure to the sun often leads to sunburn, with the skin becoming reddened and inflamed. In extreme cases, blistering and peeling occur, and this has been linked to a higher risk of skin cancer.

The sun produces visible light and other types of electromagnetic radiation that are invisible to the human eye.

Visible light consists of wavelengths in the range of 400-700 nanometers. Ultraviolet (UV) light is a shorter wavelength, higher frequency light that literally translates to ‘beyond blue’, and is in the blue end of the colour spectrum. UV ranges from 200-400 nanometers and is further broken down into three categories: UVA (320-400nm), UVB (290-320nm) and UVC (200-290nm).

UV has different properties to visible light. For instance, if a cloud blocks a percentage of visible light on a cloudy day, it will not block the same percentage of UV. Similarly, UVA, UVB and UVC have different behavioural properties such as scattering and absorption. The earth’s atmosphere blocks most of the lower wavelength UV (almost all of UVC and most of UVB), so that on most of the UV that reaches the earth is UVA (~95%), the longest wavelength UV. Because thick clouds block UVB, the amount of UVB that makes it to the earth’s surface is heavily dependent on cloud cover.

UVB induces production of Vitamin D, which is vital for bone health, the nervous system, the immune system and controlling insulin secretion. But, overexposure to UVB can have acute and harmful effects. UVB causes direct damage to DNA, which can lead to replication mutations and eventually cancer. By contrast, UVA causes indirect damage to DNA via free radicals, and this indirect damage can lead to cancer¹. While UVA appears to be less carcinogenic than UVB, it is more abundant in sunlight than UVB. Hence UVA contributes significantly to the carcinogenicity of sunlight.

Melanin is the body’s defence against UV. Upon exposure to UV, the brown skin pigment increases – suntan. Melanin can absorb and disperse UV to some degree to protect the body’s precious DNA. In general, people with darker skin are more likely to withstand greater sun exposure than fair-skinned people.

Most sunburn appears to happen near the boundary of the UVA and UVB bands. This has led to the development of the ultraviolet index or UV Index, an international standard that conveys information about the strength of UV at a given location and time, and can be found for Australia on the Bureau of Meteorology website.

Due to the thinning of the ozone layer in the mid-latitude parts of the earth, Australia has a high UV risk. Without the ozone layer to stop the sun’s powerful radiation, UV can penetrate to the earth’s surface, including through clouds. So even on a cloudy day, it’s possible to get burnt. In most parts of Australia, the UV index is high-extremely high all year around, so it’s sensible to use sun protection all year. If in doubt, check the UV index forecast before heading out.

Reflected UV can be as dangerous as direct UV. Shiny surfaces such as water and snow reflect UV and can catch bushwalkers unexpectedly, particularly if the air temperature is cool and keeping warm is more to mind rather than sunbathing. Similarly, sun exposure is a problem at high elevations because UV exposure increases with altitude. Sun exposure is also a issue in countries where the malarial medication doxycycline is taken – it makes the skin more sensitive to sunburn.

Hence, sun protection may be as important in winter as it is in summer: use a hat, sunglasses, sunscreen, and a good shirt all year round.

Clothing provides protection from the sun by the fabric blocking, scattering and/or absorbing harmful radiation. A long sleeve shirt and long pants give protection to arms and legs, and collared shirts somewhat protect the neck.

In hot conditions, it’s wise to choose materials that are lightweight, loose and can breathe easily to prevent overheating, but this goes against common thinking that thicker materials provide better UV protection.

Clothing with denser fabrics such as cotton, linen, hemp, polyester, nylon, spandex and polypropylene are more effective at blocking, scattering and/or absorbing harmful radiation. Health organisations recommend them. A study suggests that a simple see-through test is not a valid test of UV penetration¹. The reason is that in some materials visible light is scattered, but UV can still penetrate. The human eye cannot see UV, so even if all visible light is blocked, UV can still penetrate. Hence visible light transmission is not a reliable test of UV transmission.

Originally, clothing was given an SPF standard based on a measure of how long it takes for a person’s skin to burn under the material. More recently, UPF ratings were introduced giving an indication of how well a piece of fabric can block UV. UPF are now considered a more reliable measure of a fabric’s protection against UV since different skin types burn at different rates.

In practical terms, most day-to-day clothing provides moderate sun protection. A study of typical clothing worn by the general public found that around three-quarters of clothing types regularly worn would offer protection of more than SPF 15². However, for bushwalking, where sun exposure is generally higher, it may be worth considering clothing that has a certified UPF rating, which is the measure of UVA/UVB penetration for fabrics. Old or worn fabric is less likely to protect from UV.

Clothing with UPF ratings are specially manufactured materials to absorb harmful radiation. One way of doing this is to embed the material with nanoparticles that absorb the appropriate wavelengths of light. Counter-intuitively, studies have shown that washing appears to improve UV qualities of clothing³ perhaps due to the shrinking effect or because of the chemicals in washing powders. Companies now manufacture laundry products so that consumers can ‘wash’ UV protection into their clothing.

As assessing the UV index on a walk may be difficult if not impossible, a simple solution is to act as if the sun is very strong. This could mean wearing a broad brim hat with a flap at the back, a long sleeve shirt and sunscreen on most walks. People who burn easily could also wear long pants and light gloves. A cloth barrier may and often does work better than sunscreen because clothing can’t rub or sweat off and the wearer often doesn’t need to remember to put clothes on every two hours. Essentially, the more protective clothing the user wears, the need for sunscreen decreases.

To summarise, clothing may provide an effective barrier to harmful radiation from the sun. Avoid torn, old or worn clothing, and consider using materials that have certified UPF ratings.

Sunscreen is a cream or spray applied to the skin as a protective layer against the sun and is an absolute ‘must-have’ for bushwalking in Australia. It’s essential on areas of the body that are hard to protect with clothing such as the nose and ears. Sunscreen can be bought in varying strengths and styles (cream, spray) suitable for the user’s skin type and application preferences.

Sunscreen works by absorbing or reflecting the more dangerous parts of the spectrum of sunlight. Organic sunscreens are carbon-based and contain avobenzone or oxybenzone, which absorbs UV, thus preventing it from reaching the skin. Inorganic sunscreens, often zinc, scatters or reflects UV. Sunscreen is remarkably effective considering how lightweight and easy it is to apply. However, care must be taken to re-apply frequently, especially after swimming or moderate sweating.

Skin sensitivity to the sun varies between individuals, so different sunscreens work better for some people than others. Sunscreen comes various SPF ratings, measuring how much protection the wearer has from sunburn. All other things such as length of time in the sun, walking in shady forest or on treeless plains, and if protective clothing is worn being equal, sunscreen effectiveness depends on skin type and how well the sunscreen stays on the skin.

As a rough guide, people with very fair skin complexions should apply the highest possible SPF rating (50+), and people with very dark skin can get away with an extremely low SPF rating. Where possible, select a ‘broad-spectrum’ sunscreen as this protects from UVA and UVB. To cater for higher sweating, a sports-specific or water-resistant sunscreen is preferable on bushwalks.

Examine this table (adapted from hawaiiantropic.com) to match sunscreen strength to user skin type.

A medical study found that the optimal way to apply sunscreen is 15-30 minutes before sun exposure and then again after 15-20 minutes in the sun. Once this initial reapplication is done, reapply sunscreen every two hours (or as directed on the label) and sooner if sweating a lot; sunscreen is lost via sweat. On a bushwalk, it might be easy to forget the first re-application after 15-20 minutes in the sun, so aim to do it at the first break and then again at lunch and afternoon tea.

Before going on a bushwalk, it’s a good idea to test the sunscreen for allergies at home. Apply a small amount to the wrist and check regularly for unusual swelling or redness. Sunscreen has a finite life, so check the use-by date.

Sunscreen is undoubtedly a fantastic solution for sun protection, but there are environmental considerations when using it in the bush.

Some sunscreens contain UV-filtering nanoparticles. These particles are minuscule, around a thousandth of a hair diameter or one billionth of a metre. Zinc oxide is commonly used in sunscreen: it’s effective at absorbing harmful UV reports with no known side effects to human health.

However, nanoparticles may have toxic effects on marine animals with knock-on effects to whole ecosystem processes. Even at tiny concentrations, nanoparticles may interrupt essential cellular processes and make some marine species more susceptible to further contaminants.

This presents a difficult moral dilemma: to protect oneself or the environment? There is undeniable evidence that excessive sun exposure increases the risk of medical complications and sunscreen can reduce the risks, but there is equally strong evidence to show that there are environmental risks of using sunscreen.

Perhaps the solution is a compromise. For example, if the group is planning to take a swim in a creek or natural pool in a natural area, consider alternatives to sunscreen such as wearing suitable clothing or swimming in shady areas to avoid excessive sun exposure.

Broad brim hats protect the face and neck from the sun. The brim blocks UV and gives shelter from precipitation. Broad brim hats are comfortable and effective sun protection, and should be worn on all bushwalks at all times.

Hats come in many shapes and sizes, with different ways to help secure them. Some sizes, shapes and fabrics are better at providing protection than others.

Consider the following when selecting a bushwalking hat.

Size and shape
Peaked caps give minimal protection to the face and none to the ears or the neck. Broad brim hats give the best protection. As a rough guide, a 10-centimetre brim should give good protection to the head. This must be balanced against visibility by the user – some brims can obscure parts of the user’s vision, particularly peripheral vision. Hats should be loosely fitted to avoid discomfort and headaches, but not so loose that they fall off easily.

Fabric
Denser fabrics such as cotton, linen and hemp, polyester, nylon, spandex and polypropylene tend to have superior UV protection. Old or worn fabric is less likely to protect from UV. Thinner materials can their UV protection boosted with nanoparticle additives.

Weight
Natural fibres like cotton, linen and hemp are heavier than lightweight synthetics like polyester, nylon, spandex and polypropylene. Select lighter materials if the user has neck or shoulder issues that wearing heavier materials will aggravate.

Other features
A strap is useful for holding the hat in place in windy conditions or in scrub. Some hats have mesh sections to help evaporate sweat and keep the user cool. However, mesh can expose the skin to direct UV. Better to keep cool by periodically wetting the hat with water if passing close to a water source. Insect repellent mesh is sometimes built into the hat. This is useful in areas with high infestations of flies or mosquitoes but can be quite uncomfortable to use for long periods of time because it’s hard to see and breath through the mesh. Hats with side-flaps can sometimes be as effective.

In summary, a broad brim hat made from dense fabric offers the best sun protection to the head but isn’t necessarily the most practical option on a bushwalk. Lighter hats are easier to stow and are more comfortable, but users should avoid extended periods of exposure.

Most sunglasses transmit some visible light and block substantial amounts of harmful UV. Overexposure to UVB can damage the retina, cornea, lens and conjunctiva and other eye diseases, so reducing the amount of UVB reaching the eye can substantially improve long-term eye health¹.

Manufacturers of sunglasses are not compelled to follow standards for the amount of sunlight (visible and UVB) transmitted through the lenses². Consequently, cosmetic sunglasses may allow significantly higher percentages of UVB through than special purpose lenses. Care must be taken when selecting a suitable pair of sunglasses, and price or brand may not be a guarantee of quality regarding UVB protection.

Some researchers believe that the shape of the sunglasses is more important than the amount of UVB protection, claiming that the majority of ocular damage occurs from scattered or reflected light entering through the side of the glasses³. Sunglasses with side protection can be purchased on the Cancer Council website or from companies like Bollé. However, if it’s not possible to use glasses with side protection, look for a pair with lenses that cover the sides and sit close to the face.

Sunglasses are crucial when snow shoeing or skiing. Snow reflects UVB extremely effectively, and this reflected sunlight can be as damaging to eye health as direct sunlight. Sunglasses also provide protection from bright sunlight on the horizon. During winter, the sun moves closer to the horizon and sunlight is more likely to shine into the eyes. While the amount of UVB that penetrates the atmosphere decreases considerably when the sun is on the horizon, sunglasses improve comfort substantially for the user.

When selecting a pair of sunglasses, consider these aspects.

UV protection
Aim for sunglasses that blocks 99% of UV and blocks both UVA and UVB. Such sunglasses are labelled UV400.

Polarised lenses
These reduce glare from shiny surfaces such as snow, glass, and water, making it easier to see. Quickly test if sunglasses are polarised by examining the intensity of a shiny image (e.g. a computer monitor) through the sunglasses when they are held normally, and when they are turned vertically. If the reflection changes, then they’re polarised. There’s another method that can be done with one known polarised lens such as a camera filter and one that’s being tested. Hold them to the light and rotate one through 90 degrees. If the test lens is polarised the light will go black.

Frame weight
Select lightweight materials as heavy frames can give some people a headache.

Price
Titanium is a durable but expensive option. Sunnies are all too easy to break or lose in the bush, so opt for something that’s relatively inexpensive to replace.

Straps
A cord attached to both arms can hold glasses securely in place, stopping them getting dislodged or lost accidentally. Alternatively, glasses with arms that wrap around the ears to keep them in place are sufficient.

Side protection
For protection from peripheral radiation.

Some prescription glasses can be made with tinted lenses which help absorb light before hitting the user’s eyes. Although not as effective as polarised lenses at reducing glare, they do offer reasonable protection, and some people find this an easier option than contact lenses and sunnies.

To sum up, bushwalking sunglasses should be lightweight and comfortable, perhaps secured to the user’s head or body so the sunnies are hard to lose.

Staying well protected from the sun’s harmful radiation extends beyond using just physical aids such as hats, sunglasses and sunscreen. It’s about making sensible behavioral choices and decisions around how to avoid too much sun exposure.

Bushwalking involves a certain amount of being in the sun – that’s part of the fun of being outdoors – but there are ways of planning the walk to avoid too much exposure.

The solar noon is when the sun is at the highest point in the sky, and the UV is strongest. This occurs around noon to 2 pm but depends on the latitude and time and changes with season. Use the NOAA calculator to work out solar noon. On a bushwalk, especially in hot weather, aim to hit a shady spot in the middle of the day. Find a place where the group can relax, enjoy lunch and cool down before tackling the rest of the walk later in the afternoon when the sun is lower. Waiting until dusk is probably too late for most people.

A better option in hot conditions is to start early with the aim of finishing by the middle of the day or early afternoon. This may entail packing up in the dark, but it means that most of the walking is over by lunch. Knowing that there’s only an hour or two after lunch – if that – is psychologically useful on some walks.

In most parts of Australia, the UV index is extremely high for most of the year, so outdoor activities must be planned with that in mind. Take regular breaks in the shade, stay protected from the sun and keep an eye on everyone in the group to make sure they’re managing. It’s also a good idea to look for heat-related medical conditions, many of which can be avoided by drinking water and keeping cool.