A new study suggests we judge people within seconds -- and that’s just by looking at their face.

Research published in the journal Proceedings of the National Academy of Sciences shows that first impressions develop within in as little as 100 milliseconds. We quickly, and probably unconsciously, decide if people are trustworthy, dominant and even good looking based on a number of facial features.

"In everyday life I am not conscious of the way faces and pictures of faces are influencing the way I interact with people," said Dr. Tom Hartley, a neuroscientist who led the research, in a statement. "Whether in 'real life' or online; it feels as if a person's character is something I can just sense. These results show how heavily these impressions are influenced by visual features of the face -- it's quite an eye opener."

Researchers at the University of York, in England, took 1,000 ordinary photos from the Internet and showed them to at least six participants. The researchers broke each face down into 65 physical features, such as shape of jaw, mouth, eyes, cheekbones and eyebrow height. The participants rated their first impressions on 16 social traits such as trustworthiness and dominance.

The researchers then built a mathematical model for how the dimensions produce the first impressions. Using these models, the team created cartoon faces and tested more people finding the same results as the computer.

Overall, there was a tendency for a masculine face to seem more dominant, a smiling face is more approachable and trustworthy and larger eyes are more youthful. Pose, expression and lighting also play a role.

"We make first impressions of others so intuitively that it seems effortless," said Richard Vernon, a PhD candidate who was part of the research team. "I think it's fascinating that we can pin this down with scientific models."

But there are some causes for worry. "It might be problematic if we're forming these kind of judgements based on these rather fleeting impressions," Hartley told BBC. "Particularly in today's world where we only might see one picture of a face on social media and have to form our impression based on that."

Hartley added this research may be valuable to casting directors, portrait photographers or anyone posting a photo on an online dating site.

The researchers only looked at Caucasian faces for this study to avoid the possible effects of race. They are currently working on cross-cultural studies to see how culture affects the results. 

Now if someone would only create an app for that. That way if you are trying to decide if you should trust someone, you'll just have to take a picture of them and let the computer do the work.