Surprising finding emerges from psychology study on lip size and attractiveness

A new study has found that a single facial feature, the size of the lips, can alter how attractive a face is perceived to be. But the research shows that these preferences are strongly influenced by both the gender of the face being viewed and the gender of the person making the judgment, and that our standards for attractiveness can be rapidly shifted by what we have recently seen. The findings, published in the Proceedings of the Royal Society B, offer insights into the mechanisms of face perception and have implications for understanding the rise of cosmetic procedures.

The research was conducted to better understand the foundations of facial attractiveness. Judgments about a person’s appearance can influence everything from mate selection to hiring decisions and even outcomes in legal cases. Despite its importance in social interactions, the exact processes our brains use to determine attractiveness are not fully understood. Many scientific models suggest that we perceive faces as a whole, in a “holistic” manner, rather than as a collection of separate parts.

However, in the real world, people often try to enhance their appearance by focusing on individual features, using makeup, cosmetic surgery, or injectable fillers. David Alais and his colleagues at the University of Sydney and the University of Queensland sought to investigate this apparent contradiction. They wanted to know if manipulating just one local feature, the lips, would be enough to change a person’s overall attractiveness rating.

To test this, the researchers conducted a series of experiments. In the first part of the study, 32 participants, half male and half female, were shown a series of 24 different faces. Twelve of the faces were male and twelve were female, all with neutral expressions. For each face, the scientists created seven versions by digitally expanding or contracting the size of the lips in small, linear steps. This resulted in a range from significantly thinner lips to the original lips to significantly plumper lips. Participants viewed each of these 168 unique images for a very brief period and were asked to rate its attractiveness using a slider bar.

The overall results showed a clear pattern based on the gender of the face. On average, female faces received their highest attractiveness ratings when their lips were slightly expanded. In contrast, male faces were rated as most attractive when their lips were slightly contracted. This finding aligns with the idea that certain facial traits are associated with masculinity and femininity, and these traits can influence perceptions of beauty.

The researchers then analyzed the data by separating the ratings from male and female participants. This revealed a more detailed picture. The preference for plumper lips on female faces was driven almost entirely by the female participants. Women in the study gave their highest ratings to female faces with enhanced lips. Male participants, when rating female faces, did not show a preference for plumper lips; their peak attractiveness ratings were for the female faces with their original, unaltered lip size.

A parallel effect was observed for male faces. The preference for thinner lips on male faces was strongest among the male participants. Both male and female observers also tended to give higher and more consistent ratings to faces of their own gender, suggesting a greater certainty or precision when evaluating people from their own social group.

In a second experiment, the team investigated whether exposure to altered lips could change a person’s perception of attractiveness. This part of the study used a technique called visual adaptation, where prolonged viewing of a specific image can temporarily alter how subsequent images are perceived. Participants were first shown a face with either moderately expanded or moderately contracted lips for 15 seconds. Following this exposure, they rated the attractiveness of a series of faces with the full range of seven lip sizes.

The findings demonstrated a powerful adaptation effect. After being exposed to a face with expanded lips, participants’ peak attractiveness ratings shifted, and they now preferred faces with larger lips. Similarly, after viewing a face with contracted lips, their preference shifted towards thinner lips. In essence, their brain’s internal “norm” for what constituted an attractive lip size had been recalibrated by their recent visual experience.

This effect was strongest when the adaptation face and the test face were of the same person, but it still occurred when they were different people. This suggests that the adaptation can generalize across different faces, influencing our perception of attractiveness more broadly.

A final experiment was designed to probe the limits of this effect and to test theories of holistic face processing. The researchers wondered if the lips needed to be seen in the context of a full face to cause the adaptation effect. To find out, they had participants adapt to images of isolated lips, with the rest of the face masked.

They found that even adapting to just the lips was enough to shift subsequent attractiveness ratings of whole faces. This result challenges the idea that faces are processed only as a single unit, indicating that our brains can also encode and process individual features like lips separately, and that this feature-specific information can influence high-level judgments like attractiveness.

These findings align with other research into what makes lips appear attractive, while adding new dimensions. Studies have suggested that from an evolutionary standpoint, full lips in women may signal youth, health, and fertility. One study published in Plastic & Reconstructive Surgery-Global Open found that there is a “sweet spot” for lip fullness, with lips being rated as most attractive when the upper lip height was between 20% and 25% of half the total lip width. Lips that exceeded this range were often seen as unattractive. Another study in JAMA Facial Plastic Surgery identified a 1-to-2 ratio of upper-to-lower lip height as being most aesthetically pleasing. The new research builds on this by demonstrating that these baseline preferences are not fixed and can be recalibrated by recent visual experiences.

The study authors point out that the mechanism of visual adaptation, while typically useful for helping our sensory systems adjust to the environment, could have unintended consequences in modern society. “Exposure to distorted lips that have been artificially expanded beyond biological limits could initiate an iterative process whereby only further expansion to even plumper lips will be perceived as attractive to an adapted observer,” the researchers write. “Ultimately, such a process would culminate in lip dysmorphia.”

This process is thought to be similar to mechanisms involved in body dysmorphia, where exposure to unrealistically thin bodies can shift a person’s perception of what is normal and attractive. This study provides evidence that such visual adaptation is not limited to whole bodies but can apply to individual facial features as well. This implies that as people undergo cosmetic procedures, their own perception of attractiveness will likely adapt to their new appearance, potentially motivating further alterations.

The research has some limitations. The participants were university students, and the stimuli were static images viewed in a laboratory setting, which may not fully replicate real-world social perceptions. However, the findings open new avenues for understanding how we perceive faces and beauty. The authors suggest that the strong own-gender biases they observed could be a result of people having greater exposure to faces of their own gender, including their own face in the mirror, leading to a more finely tuned sense of attractiveness for that group.

“Our research highlights the subjective nature of beauty and the powerful influence of social and cultural factors,” Alais explained. “As cosmetic procedures become more accessible, it’s important to understand how these interventions can shape our perceptions and potentially lead to unrealistic beauty standards.” Future research could explore the long-term effects of this adaptation process and its potential contribution to body image disorders.

The study, “Distortions of lip size bias perceived facial attractiveness,” was authored by David Alais, Jacqueline Stephens, and Jessica Taubert.