Hill walking is the longest deliberate exposure most people take, and the one where the environment itself raises the dose. Ultraviolet increases with altitude, thin high cloud lets a great deal through, and above the cloud base you can be walking in bright sun while the valley you started in is overcast. Add eight hours, add pack straps, add the fact that mountain air is cool and moving and therefore removes every warning sensation, and you have the conditions for the classic hill sunburn: forehead, ears, nose, back of the neck, backs of the hands.
The conditions, set out plainly
A UK hill day, summit above the cloud
Conditions block- UV load
- Higher than at valley level, and rising with altitude. The Met Office UV index forecast is a valley figure and should be read as a floor rather than a ceiling on a hill day.
- Water exposure
- Low, except in rain or on a river crossing.
- Sweat
- High on the ascent, particularly under a pack and a hood.
- Friction
- High on the shoulders and the sides of the neck from pack straps, and on the face from wiping and from a hood.
- Typical duration
- Six to ten hours, frequently longer than planned.
- What fails first
- The shoulders under the straps, the sides of the neck, and the film on the face after the first hard ascent.
- Protection strategy
- A brimmed hat rather than a peaked cap, long sleeves for the ascent, film on the face, ears, neck and hands, and one deliberate reapplication at the summit, which is the natural stopping point of the day.
Altitude changes the number
The World Health Organization's guidance on the global solar ultraviolet index describes ultraviolet intensity rising with altitude, at a rate commonly cited as around ten per cent for every thousand metres. UK hills do not reach the altitudes where this becomes dramatic, but a Scottish summit day still sits meaningfully above the valley figure, and anyone taking this into the Alps or the Pyrenees is operating in a substantially stronger environment than the same hours in Britain.
The practical consequence is that the published UV index for the nearest town is a floor, not a ceiling. Our note on the UV index, latitude and altitude sets out how to read a forecast for a hill day.
Pack straps and the two bands on the shoulders
A loaded rucksack puts constant pressure and movement across the tops of the shoulders and the sides of the neck for the whole day. It is not dramatic abrasion, but it is continuous, and it removes a film in exactly the two bands that a t-shirt does not cover. Walkers frequently finish a hot hill day with a burn shaped like their own rucksack. The fix is a collared or long sleeved shirt rather than more sunscreen, because no film survives eight hours of that.
The reapplication clock
Reapplication clock: A hill day, car park at 0800, back at 1700
Loss on a hill day is driven by sweat, pack straps and time rather than by water. Mechanism only.
Why a brim beats a peak on a hill
A peaked cap shades the eyes, the forehead and part of the nose. It leaves the ears and the back of the neck fully exposed, and those are two of the highest risk sites on a walker. A full brim, or a peaked cap with a legionnaire flap, covers all four. On a long day this is the single highest value piece of kit for sun protection, because it removes the sites that are hardest to keep a film on. Our file on the scalp, ears and lips explains why these sites keep being missed.
The strategy
Plan the reapplication into the route
The summit, or the lunch stop, whichever is more reliable. One properly executed reapplication at the right point in the day is worth more than three intentions.
Use textile for anything a strap touches
Shoulders, upper back, sides of the neck. A film cannot compete with a rucksack.
Dress for the descent, not the ascent
People strip layers at the top and walk down in a vest in the strongest remaining sun of the day, on skin that has had a film abraded off it for five hours. If you are going to take layers off, that is the moment to reapply.
Carry lip protection
Wind and ultraviolet together are hard on lips, and a hill day delivers both for eight hours. Lip protection with a sun protection factor is cheap, small and almost universally forgotten.
What the label will and will not tell you
Broad spectrum
What it certifies
In the UK and EU, that the product provides ultraviolet A protection at a defined proportion of its labelled sun protection factor, in line with the European Commission recommendation on sunscreen efficacy that underpins the UVA in a circle mark. A pack carrying the UVA in a circle symbol is telling you a specific relationship between UVA and SPF has been met.
What it does not
It does not tell you the absolute level of ultraviolet A protection, only its relationship to the SPF. It does not mean equal protection across the spectrum, and it does not tell you anything about how long that protection lasts on a hill.
On a hill, ultraviolet A protection matters as much as the headline number, because you are outdoors for a full day rather than for a burst. The UVA in a circle mark is one of the few pieces of genuinely useful information on a UK or EU pack, and our standards note on the UVA circle explains exactly what it certifies.
What is not verifiable
We cannot tell you the ultraviolet index on a particular summit at a particular hour, and neither can any pack. Forecasts are produced for locations, not for ridgelines, and cloud, aspect and reflective ground all change what actually reaches you. Treat the forecast as an input, dress for more, and take the reapplication seriously rather than trying to calculate a dose you have no way to measure.
Coming down
Check the sites that always go: the ears, the back of the neck, the nose, the backs of the hands, the parting in the hair. If a burn has developed, the NHS sets out what to do about sun safety and sunburn. For anything that is changing on your skin over weeks rather than days, see a GP. We do not offer diagnostic guidance.