Amanda Holden is taking part in a contest to find Britain's most beautiful kisser in time for St Valentine's Day.
Women are being invited to press a "lippy" image on paper and send it to the judges.
The owner of the winning lipstick print will receive a £300 cosmetics gift voucher.
Miss Holden submitted her lips as the first entry.
The competition has been organised by the Royal Society of Chemistry to highlight the role of science in the cosmetics industry.
Expert Dr John Emsley said: "The requirements of a perfect lipstick are technically quite demanding. It should produce the desired colour and effect be it matt, shiny, glossy, frosted or pearlescent.
"Lipstick should cover evenly and not feel greasy, have a neutral taste, be long lasting and, of course, be nearly indelible."
The RSC said it could not specify women's prints only, but judging would be easier if men "were to resist entering".
Lips artificially enhanced with collagen would be disqualified.
A spokeswoman said: "We are trying to communicate, with a touch of glitz, the massive contribution that the chemicals industry and its scientists make to the health and wealth of this country."
The closing date for the competition is February 13. Entries can be e-mailed to PuckerThing@rsc.org, or posted to Pucker Thing, Royal Society of Chemistry, Burlington House, Piccadilly, London W1J OBA.
