Our lips say a lot, from words to kisses, whether the embraces of new lovers, friends greeting one another, or parents saying goodnight to kids.

No matter what kind of kiss, passionate or tender, they show two people are close.

So it is no wonder lips matter so much to us. And we want them to look good, whether by using make-up or through fillers, currently popular partly thanks to social media.

But can fillers be harmful, do they impact sensation, are they noticeable when you kiss? 

"Full, beautiful, sensual lips represent youth, fertility and sexual attractiveness," says Helge Jens, a German plastic and aesthetic surgery specialist.

"Rosy, full lips simply look vibrant, while thin, dry, colourless or wrinkled lips tend to symbolise illness and age."

Berlin-based psychotherapist Wolfgang Kruger adds, "Lips play a major role in our emotional life. Kissing is the best and most intimate way to create closeness."

Kisses are even more intimate and sensual than sex, he says.

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When people kiss, their faces come very close together and you feel an inner connection with the other person.

"You notice this when relationships become more difficult. The first thing to suffer is romantic kissing."

People don't always get plastic surgery, depending on local regulations, they can also get fillers from beauticians.

As a rule, they get hyaluronic acid injected into their lips. In many places, virtually anyone can do this because it does not require a prescription.

"The vast majority are young women who want to emulate a certain ideal of beauty," says Jens.

Often, women are inspired by what they see in social media.

"Patients actually come to the practice with printed pictures or mobile phone photos and say that they would like to look exactly like that."

He finds this trend problematic, as your lips need to suit your overall face.

Christiane Bayerl, director of the Clinic for Dermatology and Allergology at Germany's Helios Dr Horst Schmidt Clinics, mainly sees women who have gone through the menopause.

"Lips become narrower with age," she says, adding that sometimes, narrow lips can be perceived as pursed.

Jens and Bayerl say they use less than one millilitre of hyaluronic acid for lip correction.

Bayerl says she sometimes sends women home who already have "duck" lips and still want more, but there is then a risk their blood vessels could become blocked, she says.

Yes, and not only if you have had a lot of treatments.

"Just because the majority of treatments go well, it doesn't mean it's harmless," says Jens.

"You need to have precise anatomical knowledge to know where to inject hyaluronic acid so that it has the desired effect."

Common side effects include bruising if the needle hits a small blood vessel, says Bayerl.

"Occasionally, the result is asymmetrical and needs to be corrected with another treatment."

There is also a risk of infection and, in very rare cases, vascular occlusion, which must be treated immediately to prevent serious consequences.

That depends on how much filler has been injected into the lips. If it is within limits, you probably won't notice any difference, says Bayerl.

"If it is very pronounced, it will affect sensitivity."

That is because lips contain nerve endings that make them sensitive to heat, cold and touch.

"These are not increased by the injections, but have to spread over a larger surface area," says Jens.

Do people with full lips kiss better? Psychotherapist Wolfgang Krüger does not think so.

According to him, the way a person lives is more important.

"I think you can tell by looking at a person whether they are sensually inclined to kiss."

If someone has a lot of problems, is tense and reserved, this will eventually show in their facial features.

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"The person could seem to be a bit tight-lipped."

Lip correction can change their appearance, but it won't alter their way of life, he says.

Humans are the only species on Earth that kiss, say scientists, who have no clear answer as to why we developed this behaviour, according to Wolfgang Enard, an expert in evolutionary anthropology at the Ludwig Maximilian University in Munich.

"One leading idea is that kissing originated as a way of passing on food, such as pre-chewing."

There is also a theory that kissing serves to exchange bacteria and thus strengthen the immune system.

However, Enard sees another theory as more plausible, which in his view also explains why humans kiss, unlike their close relatives.

"In chimpanzees, social interaction is very much about grooming. They pick lice off each other."

In humans, however, the fur has disappeared, and kissing has developed as a remnant of grooming.

Whether it's a romantic kiss or a friendly kiss on the cheek as a greeting, "it's always a strong social signal." – dpa