The Internet is full of guides about improving or changing the way you dream. But with no solid understanding of how we dream, or even why, can any of them really teach us anything?

Given that all dreams are necessarily subjective, claims about “scientific” ways to influence dreaming tend to reflect a misunderstanding of what science actually does. Like most psychological phenomena, dreams can neither be reproduced or examined objectively, which means that all inquiry runs the risk of violating key parts of the scientific method.

For this reason, the most interesting studies of dreams are purely observational: Researchers interview a sizable sample about their individual visions, highlighting broad trends, patterns, and recurring details. Sometimes, they’ll make things more interesting by exposing each subject to a specific stimulus before bedtime. For example:

A Scent

In a study from 2008, researchers from University Hospital Mannheim in Germany found that exposing a participant to a specific scent appeared to significantly influence the general atmosphere of her dream. While a whiff of roses corresponded to more pleasant dreams, the smell of rotten eggs appeared to provoke negative dreams.

Intriguingly, neither roses nor rotten eggs were actually incorporated into the dreams. "There was hardly any kind of a dream dealing with smelling and tasting," lead author Boris Stuck told reporters.

Cheese

Back in 2005, NPR picked up a study by the British Cheese Board — a 100 percent real organization that seeks to educate the public about, well, cheese.  “What we found was that those who were eating blue cheese, Blue Stilton, were coming up with some quite vivid dreams,” board secretary Nigel White said in an interview. “One of the volunteers said that she dreamed of a vegetarian crocodile who was upset because he couldn't eat children. And another one dreamed that they had soldiers fighting with each other with kittens instead of guns.”

According to White, the researchers conducting the study theorized that amino acid and tryptophan found in dairy products were behind the cheese dreams. However, as Dr. Dana Smith points out in her Nature blog, no conclusive evidence has been produced so far.

Geomagnetism

Three years ago, Dr. Darren M. Lipnicki of the Center for Space Medicine in Berlin raised some eyebrows with a study purporting a link between dream strangeness and geomagnetic pull. After recording and analyzing his own dreams for nearly seven years, he compared patterns and trends with fluctuations in geomagnetic activity. A calmer magnetic field, he found, corresponded to more bizarre and vivid dreams.

It may seem weird, but another study from 1995 pointed to a similar correlation. However, the findings were also limited to a single subject — the author.

In the end, few of these studies tell us anything concrete about the way the outside world interacts with our dreams. Instead, they reaffirm what most of us knew all along: Experimenting with dreams is a one-man job. No matter how exhaustive a sample, you will ultimately be the judge of your own experience.

Sometimes, it’s more fun that way.