Lidos and outdoor pools occupy a strange position in British life. They are used intensively for a few weeks a year, by people who are not habitual outdoor swimmers, on exactly the days when ultraviolet is at its highest, for far longer than those people would normally spend outside. That combination is the whole article.
Four things that compound
1. Dwell time. A visit to a lido on a hot day is not a swim, it is an afternoon. People arrive, swim, sit, swim again, eat, sit, and leave several hours later. Compare that with an indoor session, which is generally an hour and generally has a hard stop because the lane hire ends.
2. Clothing. Swimwear covers very little, and unlike at a beach there is often no cover up worn between swims because everybody is wet and the venue is warm. Clothing is the most reliable sun protection there is, and at an outdoor pool it is largely absent, which is exactly why guidance from the NHS and Cancer Research UK, sun, UV and cancer puts shade and clothing ahead of product rather than after it.
3. The surface. A large flat water surface is reflective, and the reflected component adds to what reaches skin, particularly at angles that hit the parts of the face people never think about: under the chin, under the nose, the underside of the arms. This is covered in reflection and the water surface.
4. Timing. Outdoor pools are busiest in the middle of a hot day, which is when ultraviolet is highest. Sessions, lessons and public swims are timetabled around opening hours and school timetables rather than around the ultraviolet index, and that is a structural mismatch rather than anybody's fault.
Nothing on that list is dramatic on its own. All four at once is why lido sunburn is a category of its own.
Wet skin, cooling and the missing warning
The ordinary warning system for too much sun is discomfort: you get hot, and you move. In water, and with repeated immersion, that system is disabled. Skin is cool, there is a breeze, the water is refreshing, and the subjective signal that would normally move somebody into the shade never arrives. This is why people who would never sit in full sun for three hours will happily spend three hours at an outdoor pool.
The practical consequence is that timing and shade have to be scheduled rather than felt. That is covered in timing an outdoor session.
We do not recommend sunscreens, factors, formulations or brands, and we will not tell you how much to apply or how often, because that is product specific and it is covered by institutional guidance written for the purpose. For that, use the NHS, the British Association of Dermatologists and Cancer Research UK, sun, UV and cancer. If you have burnt, the NHS page on sunburn is the right place, and severe burning, blistering, or anybody who becomes unwell needs NHS 111 or a GP.
The water is a different problem outdoors
Sun does not only fall on swimmers. It falls on the pool, and that changes the treatment problem in ways that matter to an operator:
- Sunlight degrades free chlorine. An outdoor pool loses disinfectant to daylight in a way an indoor one does not, which has to be accounted for in the dosing regime.
- Rain dilutes and shifts the water, sometimes substantially and always without warning.
- Debris arrives continuously. Leaves, insects, grass, pollen, airborne dust, and whatever has blown in from the surrounding area.
- Bather load swings violently. An outdoor pool can go from nearly empty to at capacity in the time it takes for the sun to come out, which is a much faster change than any indoor pool experiences.
- Sunscreen input rises. Everybody at an outdoor pool is, correctly, wearing sun protection, which adds to the organic load as described in what swimmers add to the water.
Against that, outdoor pools gain one large advantage: the volatile byproducts of disinfection disperse into the sky instead of collecting above the water. That is why lidos rarely smell and why the respiratory exposure that dominates indoor halls largely vanishes.
Which problem am I actually dealing with?
Air and water. No ultraviolet worth planning for, a stable water system, and an accumulation problem above the surface that ventilation has to manage.
The swimmer's job indoors is mostly the pre swim shower. The environmental question belongs to the operator.
Ultraviolet, heat, and a less stable water system. The air problem largely disappears and is replaced by an exposure problem that lasts as long as the visit does.
The swimmer's job outdoors is substantially larger: timing, shade, clothing, product and hydration, plus the same pre swim shower.
The people who work there
A swimmer at an outdoor pool chooses to be there for an afternoon. A lifeguard at the same pool is there for a shift, in the same sun, usually in a fixed position with a required view of the water, often without shade over the chair, wearing minimal clothing because of the nature of the job. That is an occupational exposure question, not a lifestyle one, and it is covered in lifeguards and poolside staff. The Health and Safety Executive treats sun exposure for outdoor workers as a workplace issue.
What a swimmer can actually do at a lido
In the order that public health guidance puts them, which is not the order most people assume:
- Time. Arrive earlier or later. The single most effective change, and free.
- Shade. Use it between swims rather than sitting in the open because that is where the space is. Ask whether there is any, before you go, if you are bringing children.
- Clothing. A shirt and a hat between swims. Unglamorous, extremely effective, and almost universally ignored at outdoor pools.
- Product. Applied properly and reapplied after swimming and towelling, per the instructions and per NHS guidance. Fourth on the list, not first.
- Eyes. Sunglasses out of the water and goggles in it. See eyes, goggles and glare.
- Water to drink. Easy to forget when you are surrounded by it.
The reason product is fourth is not that it does not work. It is that it is the item most dependent on being applied correctly, in sufficient quantity, and reapplied, and the item most likely to be relied on as a substitute for the three above it. Guidance from Cancer Research UK, sun, UV and cancer and NICE NG34, sunlight exposure: risks and benefits consistently frames it as one part of a set rather than the answer.
Sun exposure at an outdoor pool session
Owns their own timing, clothing, use of shade where it exists, product, and getting out of the sun between swims. Owns noticing that wet skin removes the usual warning signal. Cannot create shade that is not there and cannot move the session time.
Owns the group's exposure, which is a different job from owning their own. Owns the session time where that is negotiable, the breaks, whether the group sits in shade, whether there is a shirt and hat expectation, and whether children are actually reapplying rather than being told to. Owns choosing not to run a long outdoor session in the middle of a very hot day.
Owns the physical environment: whether shade exists at all, where it is, whether it is usable and free, opening hours, drinking water, and shade for staff. Owns the water treatment that has to cope with sunlight, weather and swinging bather load.
Where a duty attachesGeneral guidance from the NHS, Cancer Research UK, sun, UV and cancer and NICE NG34, sunlight exposure: risks and benefits, with the ultraviolet index framework from the WHO. Staff exposure sits under the Health and Safety at Work etc. Act 1974 with HSE guidance for outdoor work.
The summary
An outdoor pool is a good place to be and this article is not an argument against going. It is an argument for recognising that a lido afternoon is a long outdoor exposure disguised as a swim, and that the disguise is effective because wet skin does not feel hot. Plan the afternoon rather than the swim, put shade and timing ahead of product, and if you are running a group, make the decisions for them before you arrive rather than at the poolside when everybody is already in.