Slop On Sunscreen

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.

Skin complexion: Very fair
Sun's effect on skin: Always burns, never tans
Recommended SPF: 30-50+

Skin complexion: Fair
Sun's effect on skin: Always burns, tans minimally
Recommended SPF: 30-50+

Skin complexion: Light
Sun's effect on skin: Burns moderately, tans eventually
Recommended SPF: 15-30

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.

Environmental impacts ⌄

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.
Interestingly, it comes down to an aesthetics argument. Both zinc oxide (as used in old style zinc cream) and titanium dioxide (common pigment in all white paints) are, generally, pretty safe to use topically and both act by simply reflecting light, including UV wavelengths. The problem? You can see them! That is, where you apply them they look white ,or coloured if coloured pigments are added (i.e. pink zink). You will notice many cricketers still using white sunscreens.


But these are not aesthetic enough for some people so manufacturers switched to microscopic forms (nanoparticles). So, if you are concerned about nanoparticles, you should an opaque product such as the old zinc cream OR a non-pigmented one that uses synthetic organic UV filters which have a very good safety record.