There is no such thing as a safe tan, a health watchdog has warned as it published new guidance on the risks and benefits of sunlight.
The report, from the National Institute for Health and Care Excellence (Nice), said adults need between six and eight teaspoons (35ml) of sun cream per application and should always aim for an SPF of 15 or higher.
It said "there is no safe or healthy way to get a tan from sunlight", adding that a tan provides little protection against further exposure to the sun.
And it said while people should expose their arms and legs to the sun for short periods in order to build up vitamin D, this had to be balanced against the risks of skin cancer.
Nice said it was not possible to get enough vitamin D by sitting next to a closed sunny window and it was also not possible to get enough vitamin D from sunlight between October and March in the UK.
It stopped short of recommending a specific amount of time people should stay out without sun cream to build up vitamin D, but said experts agreed that "short (less than the time it takes for skin to redden or burn), frequent periods of sunlight exposure are best for vitamin D synthesis."
It said this type of exposure is also "less likely to result in skin cancer".
Many adults in Britain have low levels of vitamin D (23% aged 19 to 64 and 21% aged 65 and over), as do 14% of children aged four to 10 and 22% of children aged 11 to 18.
Low levels of vitamin D are linked to musculoskeletal conditions such as rickets - which is re-emerging among children - and lack of muscle strength and function.
In the wide-ranging guidance, Nice warns that applying sunscreen too thinly reduces the amount of protection it gives.
Higher SPFs - such as 30 - may offer better protection but do "not necessarily mean people can spend more time in the sun without the risk of burning".
Nice said sunscreens should be "re-applied liberally, frequently and according to the manufacturer's instructions", including after being in the water (even if it is water-resistant) and after towel drying, sweating or when it may have rubbed off.
Sunscreen should also be applied twice if people are going to be out long enough to risk burning - once half an hour before going out, and again around the time they go out in the sun.
Groups of people who should take extra care to avoid skin damage and skin cancer include babies and children, those with fair skin or hair, people with lots of moles or freckles and those with a family history of skin cancer.
The advice also states that babies under six months of age should be kept out of direct strong sunlight and that children and young people need their skin protecting between March and October.
"They should cover up with suitable clothing, be encouraged to spend time in the shade (particularly between 11am and 3pm) and wear sunscreen," the guidance added.
Research has shown that children are particularly at risk from sunburn. Getting burnt five or more times as a child increases the lifetime risk of melanoma skin cancer by 80%.
Professor Gillian Leng, deputy chief executive and director of health and social care at Nice, said: "How much time we should spend in the sun depends on a number of factors including geographical location, time of day and year, weather conditions and natural skin colour.
"People with lighter skin, people who work outside and those of us who enjoy holidays in sunny countries all have a higher risk of experiencing skin damage and developing skin cancer.
"On the other hand, people who cover up for cultural reasons, are housebound or otherwise confined indoors for long periods of time are all at higher risk of low vitamin D levels."
Sarah Williams, Cancer Research UK's health information manager, said: "While we all need some sun for vitamin D, it's important not to overdo it as the sun's UV rays also increase skin cancer risk. Far from being a sign of health, a suntan actually means your skin is trying to protect itself from too much UV – and sunburn means that the DNA in your skin cells has been damaged. Over time, this damage can build up and lead to skin cancer.
"The UK sun isn't likely to be strong enough to cause problems in February, but if you're heading abroad for winter sports or sun make sure you protect your skin."