A health watchdog has told people there is no such thing as a safe tan as the actor Hugh Jackman announced his fifth skin cancer has been removed.
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 comes as Jackman took to Twitter and Instagram to warn fans of the dangers of not wearing sun cream.
He also appealed to people to get regular skin checks as he posted a picture of himself with a plaster on his nose after having a fifth skin cancer removed.
The Australian actor, who starred as the Wolverine in the X-Men film series, said: "An example of what happens when you don't wear sunscreen. Basal Cell. The mildest form of cancer but serious, nonetheless. PLEASE USE SUNSCREEN and get regular check-ups."
Jackman had his first skin cancer removed in 2013 after his wife, Deborra-Lee Furness, suggested he should get a mole on his nose checked.
At the time, he wrote on social media: "Deb said to get the mark on my nose checked. Boy, was she right! I had a Basal Cell Carcinoma. Please don't be foolish like me. Get yourself checked. And USE sunscreen!!!"
In its new guidance, Nice 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.
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.
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.
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."