There is no safe or healthy way to get a tan from sunlight, new guidance from the National Institute for Health and Care Excellence (NICE) has warned.
The health watchdog's latest guidance also says an existing tan provides little protection against sun exposure.
It recommends using at least factor 15 sun cream, with adults urged to use 6-8 teaspoons (35ml) per application.
Benefits from building up vitamin D from the sun have to be balanced with the risks of skin cancer, it adds.
It comes as Hollywood star Hugh Jackman has spoken out about his own experience with skin cancer. The Australian actor has had several sun-related cancerous growths removed from his face in recent years.
He posted a Facebook message urging his friends and followers to get regular skin checks and wear sunscreen.
Many adults in Britain have low levels of vitamin D and the NICE guidance states that some exposure to sunlight can help to build this up.
NICE also says it is not possible to get enough vitamin D by sitting next to a closed sunny window, or from sunlight between October and March in the UK.
However, experts stopped short of recommending a specific amount of time people should stay out.
In wide-ranging guidance they recommended:
- People expose their arms and legs to the sun for short periods in order to build up vitamin D
- 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 should take extra care in the sun
- Higher factor sun creams - such as factor 30 - may offer better protection but do "not necessarily mean people can spend more time in the sun without the risk of burning"
- Applying sunscreen too thinly reduces the amount of protection it gives
- Sunscreens should be re-applied after being in the water, after towel drying, sweating or when it may have rubbed off
- Cream should also be applied twice - once half an hour before going out and again before going in the sun - if people are going out long enough to risk burning
- Babies under six months of age should be kept out of direct strong sunlight and children need sun protection between March and October
Professor Gillian Leng, 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."