Midriff-baring tops and backless dresses could be harming young women's health, experts have warned.
Popstars like the Pussycat Dolls are fans of the midriff-baring look
Lancashire health bosses say, if body heat is low, people have a higher risk of illnesses and infections.
And going out on a chilly winter night in clothes more suited to "Ibiza" could lead to hypothermia, they say.
A spokeswoman for Burnley, Pendle and Rossendale Primary Care Trust, which issued the advice, denied they were being "killjoys".
'Wrap up warmly'
Catriona Logan, the PCT's Service Provision Director, says: "We know that fashion dictates what younger people wear, but it is a proven fact that if people get cold, they are more likely to catch a cold, or some other bug or infection.
"The current fashion is for girls to bare their midriffs, or have backless dresses.
"That's very nice for inside wear or if you're in the sunshine state of Florida or in Ibiza, but it's a bit chilly in the night air during winter, especially if they are coming out of a warm environment like a pub or a club."
She added: "Summer-style clothes are fine if you are inside, but our advice is to wrap up warmly when you go out.
"Yet a lot of young girls don't seem to bother.
"The message is the same for men too, in that thin T-shirts are ok for indoors, but wear a jacket or coat outside.
"It's entirely up to each individual of course, but that's our advice."
Maggi Morris, director of public health for Preston PCT, added: "Normally we target out advice towards elderly people, but young people are at risk too.
"If you're exposing large areas of your body, and drinking alcohol, your body temperature goes down, and you are increasing your risk of hypothermia.
"Your body temperature only needs to go down to 35 degrees Celsius for that to happen."
She said it may be unrealistic to expect teenagers and young women to wear coats.
But she suggested they wear shrugs or capes, which are currently in fashion - and that they ensure they are not going to have to walk home in the cold after their night out.
Researchers at the Common Cold Centre at Cardiff University last month published a study showing people became more susceptible to illness if their body temperature was lowered
Half of 180 volunteers were asked to keep their bare feet in icy water for 20 minutes.
They found 29% developed a cold within five days, compared with only 9% in the control group not exposed to a chill.
Professor Ron Eccles, the centre's director, told the Daily Mail: "When I see students with bare midriffs in November, it's obvious they don't take it seriously.
"They are asking for trouble."