Ask a regular at any municipal pool why they keep coming back and you will rarely hear the word “cardio”. They talk about sleeping better, about the knee that no longer aches, about the half hour a day when nobody can reach them by phone.
Swimming is one of the few forms of exercise that suits almost everyone, from a toddler in a warm teaching pool to an eighty-year-old doing slow breaststroke at 7am. This guide looks at what the evidence says about swimming and health, how it compares with running for weight loss, what to eat beforehand, and how to deal with the less pleasant side of the pool: chlorine.
If you have a specific question about breathing, goggles, ear water or swimming on your period, our swimming questions answered guide covers those one by one. More health and fitness features live in our Wellbeing section.
Why swimming is good for you
The NHS recommends that adults do at least 150 minutes of moderate activity a week, or 75 minutes of vigorous activity, plus strength work on two days. Its list of vigorous activities includes swimming, alongside running and football. Water aerobics appears on the moderate list.
That matters, because it means three steady 25-minute lane swims a week meet the official target for vigorous exercise.
The water does much of the rest. It supports your body weight, so there is none of the pounding that running puts through ankles, knees and hips. That makes swimming a sensible option for people who are overweight, recovering from injury, pregnant or living with stiff joints, though anyone with a medical condition should check with their GP first.
Water is also roughly 800 times denser than air, so every stroke is a form of resistance work. Swimming will not build muscle like a weights room, but it works the shoulders, back, core and legs together.
Swim England’s 2017 report on the health and wellbeing benefits of swimming found evidence that swimmers live longer, and that swimming has a positive impact on people with mental health conditions. Many swimmers would recognise the second point: the rhythm of breathing and the absence of screens make a swim one of the calmer parts of the day.
How to lose weight swimming
Swimming burns a useful number of calories, but how many depends on your weight and how hard you work. Harvard Health Publishing’s widely used table gives these estimates for 30 minutes:
| Activity (30 minutes) | 125lb (57kg) | 155lb (70kg) | 185lb (84kg) |
|---|---|---|---|
| Swimming, general | 180 | 216 | 252 |
| Swimming laps, vigorous | 300 | 360 | 420 |
| Running at 5mph (12 min/mile) | 240 | 288 | 336 |
| Running at 7.5mph (8 min/mile) | 375 | 450 | 525 |
Effort is everything. A leisurely breaststroke with your head up burns far less than continuous front crawl, and butterfly burns the most of all, if you can keep it going.
The practical lesson is that swimming needs to be structured to work for weight loss. Rather than drifting up and down, try intervals: for example, four lengths fairly hard, a 30-second rest at the wall, four lengths easy, repeated for 20 minutes. Use a kickboard or pull buoy to work legs and arms separately, and switch strokes to keep it interesting.
Running or swimming: which burns more calories?
On Harvard’s figures, running at a steady pace burns somewhat more than vigorous lap swimming for the same person in the same 30 minutes, and a lot more than gentle swimming.
That is not the whole story. Swimming is far kinder to the joints, which means many people can swim more often, and for longer, than they could run without getting injured. The best exercise for weight loss is the one you will actually keep doing three or four times a week.
Why am I so hungry after swimming?
Many swimmers notice they are ravenous when they get out of the pool, and it is easy to undo a session with a large hot chocolate and a pastry in the leisure centre café.
Researchers have not pinned down a single cause, though cool water and the effort itself are both likely to play a part. Whatever the reason, the answer is to plan for it. Pack a snack such as a banana, yoghurt or a slice of wholemeal toast with peanut butter, and keep it to that. Weight loss still comes down to using more energy than you take in.
What to eat before swimming
You have probably heard that you must wait 30 minutes after eating before swimming. There is no good evidence that eating causes swimmers to drown. The worst that usually happens is discomfort or a stitch if you swim hard on a full stomach.
What and when you eat should depend on how long you have before your swim.
Two to three hours before: a normal meal with carbohydrate and some protein works well. Think scrambled eggs on toast, a chicken or tuna sandwich, a jacket potato with beans, or a rice bowl with vegetables.
About an hour before: something lighter. Porridge or cereal with milk, yoghurt with granola, or toast with a little peanut butter.
Thirty minutes before or less: a small, easily digested snack. A banana, a cereal bar or a slice of malt loaf.
Foods with a lower glycaemic index, such as porridge and wholegrain bread, release energy slowly and suit longer sessions. Quicker-release foods like a banana are better when time is short.
For an early morning swim, many people do perfectly well on nothing more than a glass of water and a banana, then eat breakfast afterwards. And drink water. You sweat in the pool even if you cannot feel it.
Chlorine: what it does and why the pool smells
Chlorine is added to pools to kill bacteria and other germs. It works well, but it reacts with everything swimmers bring in with them: sweat, skin cells, cosmetics and, unfortunately, urine.
What is free chlorine?
“Free chlorine” is the chlorine still available in the water to disinfect it. When it reacts with sweat and other waste, it forms “combined chlorine”, mainly compounds called chloramines, which no longer disinfect well.
Pool operators test both levels throughout the day. In the UK, the Pool Water Treatment Advisory Group (PWTAG) sets the industry’s code of practice, and its guidance states that if disinfectant levels fall outside the required range, the pool must be closed until they are corrected.
Here is the surprise: that strong “swimming pool smell” and red, stinging eyes are usually signs of too many chloramines, not too much chlorine. PWTAG lists high combined chlorine from bather pollution as one of the main causes of smell and irritation, and pre-swim hygiene as part of the fix.
So the single most useful thing any swimmer can do for the water is take a quick shower before getting in.
A quick check before you swim
You do not need a testing kit to get a sense of a pool. Ask yourself a few simple questions:
- Can you see clearly to the bottom, including the lane lines and the drain?
- Do the walls and the edges feel smooth rather than slimy?
- Is there a sharp chemical smell? If so, mention it to staff.
- Is there a lifeguard on duty and is the pool reasonably clean?
And try not to swallow the water, however clean it looks.
How to remove chlorine from skin and hair
Chlorine can strip the natural oils from your skin and hair, leaving them dry, tight or itchy, especially after frequent sessions.
Shower straight away. Rinse thoroughly with warm water and a mild soap or shower gel, paying attention to your hair and scalp. Don’t wait until you get home.
Moisturise while your skin is still slightly damp. A simple, fragrance-free moisturiser works as well as anything marketed specifically to swimmers.
Look after your hair. Wet it with clean water before you swim and wear a cap. Afterwards, wash it with shampoo and use conditioner. Swimmers’ shampoos claim to remove chlorine and the minerals that can give fair hair a greenish tint, and some swimmers find them helpful.
Vitamin C sprays. Vitamin C (ascorbic acid) neutralises chlorine in water, which is why it is used in some shower filters and in “anti-chlorine” sprays sold to swimmers. Whether these make a noticeable difference to your skin is less clear, and there is little independent research on it. They are unlikely to do harm, but a good rinse and moisturiser come first.
If you have eczema. Chlorine can aggravate it. Many people with eczema find it helps to apply a thick layer of their usual emollient before swimming, to act as a barrier, then rinse off well and reapply afterwards. Ask your GP, pharmacist or dermatology nurse for advice that suits your skin.
Swimming with stretch marks
Stretch marks are extremely common. The NHS describes them as harmless and says they are usually linked to sudden growth or weight change, such as during pregnancy, puberty or rapid weight gain or loss. They usually fade and become less noticeable over time, although they may not disappear completely.
The NHS is also frank that there is very limited evidence that creams and lotions prevent or remove them. Laser and light treatments may improve how they look but are not usually available on the NHS.
Most swimmers simply stop noticing them, and so does everyone else in the pool. If you would feel more comfortable covered up, there are plenty of choices:
- A one-piece costume covers the stomach and stays in place during lengths.
- High-waisted bikini bottoms cover the lower stomach while keeping a two-piece look.
- Swim shorts, leggings or skirted bottoms cover the upper thighs.
- A rash vest, short or long-sleeved, covers arms and torso and adds sun protection outdoors.
Open water and cold water swimming
Lidos, lakes and the sea have become hugely popular, and many people say a cold dip lifts their mood. Cold water also carries real risks, chiefly cold water shock: the involuntary gasping and rapid breathing that can follow sudden immersion.
The RLSS UK “Float to Live” advice is the one to remember. Lean back with your ears in the water, try to control your breathing, spread your arms and legs, and scull gently until the gasping passes. Then swim to safety or call for help.
At the coast, the RNLI says to swim between the red-and-yellow flags, and to stay out of the water altogether if a red flag is flying. If you are drawn to waves, our beginner’s surfing guide covers the basics, and our surf trips guide suggests where to try it.
Getting started
If you have not swum for years, start small. Two lengths of breaststroke and a rest at the wall is a perfectly good first session. Add a length or two each time.
Many leisure centres run adult lessons and “improver” sessions, and lane swimming times are usually listed by speed. Pick the slow lane at first, swim clockwise, and let faster swimmers pass at the wall.
You need very little kit: a costume, goggles and a towel. If you want to upgrade later, our sailing and surf gear guide rounds up kit for life on and in the water.
Frequently asked questions
How often should I swim to lose weight?
Three or four sessions a week of 30 minutes or more, at an effort that leaves you slightly breathless, is a realistic target. Pair it with sensible eating, as swimming alone will not offset a diet with too many calories.
Is swimming better than walking for weight loss?
Vigorous swimming burns considerably more than a gentle walk in the same time. Brisk walking is easier to fit into a day, though, so many people do both.
Does swimming tone your stomach?
Swimming works the core muscles that hold your body straight in the water, but you cannot lose fat from one area alone. A flatter stomach comes from overall fat loss.
Is swimming good for bad knees or back pain?
The water supports your weight, so many people with joint or back problems find swimming comfortable. Breaststroke kick can strain some knees, so try front crawl or backstroke instead. Check with your GP or physiotherapist if you have a diagnosed condition.
Can I swim every day?
Yes, if you vary the intensity and your body feels fine. Mixing hard sessions with easy ones helps prevent shoulder strain.
Should I eat before a morning swim?
Not necessarily. A banana or a small snack is enough for most people doing a short session, with a proper breakfast afterwards.
Why does my skin itch after swimming?
Chlorine strips natural oils from the skin. Shower straight after your swim and apply moisturiser. If the itching is severe or comes with a rash, speak to a pharmacist.
Is it bad to swallow pool water?
A little will not usually hurt, but pool water can carry germs that chlorine does not kill instantly. Try not to swallow it, and stay away from the pool if you have had diarrhoea recently, so you do not pass a bug on to other swimmers.
Does chlorine make your hair go green?
It is mostly copper and other minerals in the water, which chlorine helps bind to the hair, that cause the green tint. Wetting your hair first, wearing a cap and washing it afterwards all help.
Is swimming good for mental health?
Swim England’s 2017 report found that swimming has a positive impact on mental health conditions. Many swimmers describe it as the most peaceful part of their week.
