Reminiscing about the past is something that everyone, including myself, engages in quite frequently. I’m the first to admit that I spend more nights than I should replaying fond memories over and over in my head, wishing I could go back and relive them just one more time--and I know I’m not the only one. I mean, how could we not yearn for days of childhood, when we were younger and had no responsibilities? How can we not think about times when the world seemed so much simpler and brighter? It’s easy to slip into the warm embrace of yesterday, especially when the uncertainties and complexities of present-day seem too much to handle.

But why do we romanticise the past so much, and idealize it more than the present or future? Perhaps because it masks the truth of reality, or because it helps people cope with memories that are otherwise painful to remember.

However, as it turns out, the feeling of nostalgia encompasses much more than just dramatically looking out the window and wishing you could turn back time. It's about more than simply missing someone or something--the real phenomenon of nostalgia is based less on subjective feelings, and more on science.

Why do we feel nostalgic?

Alan R. Hirsh wrote in "Nostalgia: A Neuropsychiatric Understanding" that nostalgia is not an emotional state, but rather a longing for a sanitized impression of the past. In psychoanalysis, this "sanitized impression" is referred to as screen memory, which is not a true representation of memory. Rather, it is a conglomeration of many different memories, ones that filter out negative emotions to integrate positive emotions instead. We take these positive emotions attached to a specific memory or era of life and idealize them, to seem better than they actually were.

We can apply these happy, comforting feelings to inanimate objects, places or even smells--Sigmund Freud theorized in 1908 that odor was strongly linked to such feelings, because the nose is connected to the olfactory lobe in the limbic system of the brain, which is believed to house emotions.

Director of the Laboratory Cognitive Neurobiology at Boston University Howard Eichenbaum told NBC in 2015, “Olfactory has a strong input into the amygdala, which processes emotions. The kind of memories that it evokes are good and they are more powerful,” he said.

Also residing in the limbic system is the hippocampus, which is critical to developing both emotion and memory. These two connections explain why certain smells, when they reach the limbic system in the brain, can incite even the most intense nostalgic feelings.

According to a 2015 study, the average person can distinguish between trillions of odors, and interpret each one in a uniquely personal way. Thus, how we associate certain smells with our lives and react to them can be vastly different--the smell of cow manure might disgust some people, but it would elicit feelings of nostalgia from others who might have lived on a farm when they were a child.

Is nostalgia good or bad for us?

In the 17th century, nostalgia used to be considered a mental disorder--Swiss physician Johannes Hofer coined it to be a cerebral disease when attempting to diagnose Swiss soldiers who desperately missed home. Now, however, the feeling of nostalgia is seen as a socially acceptable comfort, and sometimes even encouraged. Professor David Gerber of the University at Buffalo noted in his studies that society has only just recently begun to recognize nostalgia as a beneficial force. “There are positive uses to which memory, even painful memory, may be put in the effort to confront the challenges to personal identities of such massive changes in the lives of an individual,” Gerber said in an interview with Reporter Magazine in 2015.

This in particular makes sense of why young adults seem to be the most nostalgic of them all--young adults can face frequent periods of change, such as leaving home to go to college or moving to a different city. Nostalgia can be helpful in counteracting negative feelings like anxiety, depression and loneliness that stem from life’s turbulence. It has adaptive functions that can offer much-needed context and direction, to remind us of previous positive experiences, and ones that are yet to come. Nostalgia can also improve levels of empathy and make us better communicators, as it is felt universally by all ages, cultures, races or genders. No one shares the same memory, of course, but everyone can relate to feeling nostalgic and yearning for the good old days.

It can even cause our body temperatures to rise, suggested in a study by Xinyue Zhoe of Sun Yat-Sen University in southern China. The study tracked students over the course of one month, and found that feelings of nostalgia were most common on colder days and in colder rooms. Participants in the study who reported feeling nostalgic also reported feeling warmer, which illustrates a potential link between being able to recruit a memory and maintaining physiological comfort.

The past is similar to the future in some ways; it is just as elusive and difficult to fully grasp. It is often distorted by anxiety or stress, and it idealizes what we want to remember something as, instead of what it truly is. But feeling nostalgic of the past isn’t all bad, and can have some surprising benefits on our overall mood and psyche. It can help us adjust to new situations, counteract anxiety or depression and connect us to others who may be feeling the same way. Just be careful what you yearn for, and remember to take off the rose-colored glasses once in a while--perhaps the present day isn’t as bad as nostalgia makes it out to be.