Experts believe women with a more prominent tubercle, that's the middle part of the top lip that points upwards - such as Angelina Jolie and Megan Fox have - are getting more fun in bed.
But are your lips also sending warning signals about your health?
Dry or sore lips could indicate anything from diabetes to herpes or Crohn's disease.
Dermatologist Shona Birch, who runs a private practice in Sevenoaks, Kent, said: "Really hot or cold weather could leave you with dry or cracked lips.
"But it could also be down to something more serious. If symptoms persist and you can't find a reason for it, then it's best to consult a pharmacist or a GP.
"There are lots of things you can do to keep your lips healthy. Use a lip balm with a protective sunscreen.
"Try not to lick your lips when it's cold - it will only make them dryer.
dryer."And use a petroleum jelly before you go to bed at night to keep them moist."
Here, Sun Health tells you what to look out for... and explains why you should listen to your lips.
Cracked lips
Could mean: Diabetes
Cracked lips are very common and in most cases may be due to nothing more than a mild case of anaemia.
This leads to open cracks or sores in the corner of the mouth - a condition doctors call angular cheilitis.
But in isolated cases it could be a sign of undiagnosed diabetes. As blood sugar levels rise, this stimulates the growth of a fungus that can attack the lips.
Swollen lips
Could mean: Crohn's disease
Most people know that Crohn's disease affects the bowel. But it can also show up in the mouth and lips.
The condition, which affects one in every 1,000 people in Britain, can cause inflammation and swelling in different parts of the body, including the lips.
It even has its own name - oral Crohn's. Around ten per cent of Crohn's sufferers are also affected around the mouth.
Burning lips
Could mean: Herpes
A burning sensation on the lips can be one of the first signs of an outbreak of the herpes virus, which causes cold sores.
Within 24 hours, blisters may start to appear on and around the lips which are painful and, after a few days, they can burst and leak contagious fluid.
Avoid touching these sores, kissing or even sharing soaps, flannels or lipstick.
Numb lips
Could mean: Severe allergy
Numbness or tingling in the lips, especially if it is rapidly followed by swelling, could be a sign of a severe allergic reaction to a food or chemical.
Doctors call this angiooedema and it means the body is releasing huge amounts of the hormone histamine into the bloodstream in an over-reaction by the immune system.
Blue lips
Could mean: Croup
Going blue around the mouth and lips is a sure sign of a lack of oxygen.
In babies, it can be a symptom of croup, a respiratory condition that causes a hoarse, barking cough.
In adults, blue lips are often a symptom when the heart is struggling to pump oxygen-rich blood around the body, for example in people who suffer from chronic heart failure.
Lip rash
Could mean: Eczema
A rash around the edge of the mouth is often due to dry skin caused by excessive lip licking or thumb-sucking.
Dubbed "lick eczema", it should clear up when the habit stops and also responds to regular applications of one per cent hydrocortisone cream for a few days.
Coldsores
Could mean: Poor diet
A poor diet, stress or lack of sleep is often a strong trigger for cold sore outbreaks.
You should also avoid foods and drinks rich in an amino acid called arginine, such as peanuts, cashew nuts, chocolate, beer and cola.