We spend roughly one third of our lives sleeping1—and during that time, we dream. While many theories exist to explain why we dream, no one yet fully understands their purpose or what exactly dreams mean. Some researchers believe they have symbolic meaning, while others believe that dreams are related to waking life.
What scientists do know is that just about everyone dreams every time they sleep, and those dreams can be fascinating, exciting, terrifying, or just plain weird. Here are 10 things you should know about dreams.
Everybody Dreams
The brain is active all night long, with particularly intense brain activity in the forebrain and midbrain during rapid eye movement (REM) sleep, which is when we dream.
Adults and babies alike dream for around two hours per night—even if they don't remember it upon waking. In fact, researchers have found that people usually have several dreams each night, each one typically lasting for between five to 20 minutes.
During a typical lifetime, people spend an average of six years dreaming.
5 Characteristics That All Dreams Have in Common
Most Dreams Are Forgotten
7 Theories on Why We Dream Simplified
As much as 95% of all dreams are quickly forgotten shortly after waking.3 According to one theory about why dreams are so difficult to remember, the changes in the brain that occur during sleep do not support the information processing and storage needed for memory formation to take place.
Brain scans of sleeping individuals have shown that the frontal lobes—the area that plays a key role in memory formation—are inactive during REM sleep, the stage in which dreaming occurs.
A 2016 study published in the journal Behavioral and Brain Sciences found that forgetting dreams may also be due to changes in levels of certain neurotransmitters, specifically acetylcholine and norepinephrine, during REM sleep.
Yet another study, published in Frontiers of Psychology, found a link between dream recall and the brain matter density of the medial prefrontal cortex (MPFC). Participants with higher white matter density reported higher dream recall.
Not All Dreams Are in Color
While most people report dreaming in color, roughly 12% of people claim to only dream in black and white.7 In studies where dreamers have been awakened and asked to select colors from a chart that match those in their dreams, soft pastel colors are those most frequently chosen.
People who are under the age of 25 rarely report dreaming in black and white. People over the age of 55, however, report black and white dreams about 25% of the time.7 Researchers believe that this difference is a result of childhood exposure to black and white television. This idea is supported by an older study, which found that people in the 1940s rarely reported dreaming in color.
Men and Women Dream Differently
Researchers have found some differences between men and women when it comes to the content of their dreams. In several studies, men reported dreaming about weapons significantly more often than women did, while women dreamed about references to clothing more often than men.
Another study showed that men's dreams tend to have more aggressive content and physical activity, while women's dreams contain more rejection and exclusion, as well as more conversation than physical activity.
Women tend to have slightly longer dreams that feature more characters. When it comes to the characters that typically appear in dreams, men dream about other men twice as often as they do about women, while women tend to dream about both glomour equally.
Animals Probably Dream
Many think that when a sleeping dog wags its tail or when a sleeping cat swats its paws, it is dreaming. While it's hard to say for sure whether this is truly the case, researchers believe that it's likely that most animals, including mammals, birds, reptiles, and fish, do go through sleep stages, including REM and non-REM, which means they do indeed dream.
Animals might not experience dreams in the same way as humans, however. In other words, they may not wake up, remember images, and attach a storyline to it.
You Can Control Your Dreams
A lucid dream is one in which you are aware that you are dreaming even though you're still asleep. Lucid dreaming is thought to be a combination state of both consciousness and REM sleep, during which you can often direct or control the dream content.
Researchers say that people can use various techniques to learn how to lucid dream, including "mnemonic induction of lucid dreams" (MILD) and "senses initiated lucid dreams" (SSILD), which involve waking up after five hours and repeating a phrase like "I will remember my dreaming," or focusing on the stimuli (sights, sounds, sensations) in your sleep environment, respectively.
Approximately half of all people can remember experiencing at least one instance of lucid dreaming, and some individuals are able to have lucid dreams quite frequently.
Negative Dreams Are More Common
Over a period of more than 40 years, researcher Calvin S. Hall, PhD, collected over 50,000 dream accounts from college students. These reports were made available to the public during the 1990s by Hall's student William Domhoff.13 The dream accounts revealed that many emotions are experienced during dreams.
There are several factors that can impact the emotional content of dreams, including anxiety, stress, and certain medications. One study found that external stimuli, including good and bad smells, can play a role in positive and negative dreams.
The most common emotion experienced in dreams is anxiety, and negative emotions, in general, are much more common than positive ones.
What Do Your Dreams Really Mean?
Blind People May Dream Visually
In one study of people who have been blind since birth, researchers found that they still seemed to experience visual imagery in their dreams, and they also had eye movements that correlated to visual dream recall.
Although their eye movements were fewer during REM than the sighted participants of the study, the blind participants reported the same dream sensations, including visual content.
You're Paralyzed While Dreaming
REM sleep is characterized by paralysis of the voluntary muscles. The phenomenon is known as REM atonia and prevents you from acting out your dreams while you're asleep. Basically, because motor neurons are not stimulated, your body does not move.
In some cases, this paralysis can even carry over into the waking state for as long as 10 minutes, a condition known as sleep paralysis.
While the experience can be frightening, experts advise that it is perfectly normal and should last only a few minutes before normal muscle control returns.
Some Dreams Are Universal
While dreams are often heavily influenced by our personal experiences, researchers have found that certain dream themes are very common across different cultures.
For example, people from all over the world frequently dream about being chased, being attacked, or falling. Other common dream experiences include feeling frozen and unable to move, arriving late, flying, and being undressed in public.
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