When thinking about sleep and its relationship to the senses, few people immediately think of smell. Sight, sound, and touch typically receive more attention because of the obvious ways that light, noise, and comfort can impact sleep.
While it might not be as immediately apparent, smell can directly affect sleep. Even though smells don’t usually cause a person to wake up, the sense of smell and sleep have a multifaceted relationship.
Aromatherapy with distinct scents may promote better sleep, help you wake up in the morning, or even influence dreams and memory formation during sleep. Circadian rhythms, part of your biological clock, help regulate your sleep and influence your sense of smell as well.
The connections between smell and sleep are subject to continuing research, but knowing about what has been discovered so far provides opportunities to make your bedroom environment more conducive to quality sleep.
How Does the Sense of Smell Work?
Your sense of smell is part of a complicated olfactory system. Special cells in the nose, called olfactory neurons, receive chemical signals from all kinds of compounds in our environment. These neurons are directly connected to the brain, allowing for rapid identification of smells based on which neurons are stimulated.
Scents can reach neurons through the nostrils or from the back of the throat, which is part of why taste and smell are intricately connected. Nerve endings in other parts of the body can also contribute to smell through the common chemical sense, which helps detect irritating compounds.
Can Certain Smells Help With Sleep?
Because of the power of the sense of smell, certain fragrances may contribute to better sleep. Some scents promote relaxation that makes it easier to fall asleep and have a well-rested feeling the next day.
Smells aren’t simply detected and identified; they can produce both psychological and physiological responses. When a pleasant smell makes you feel relaxed or a foul smell makes you queasy, you’re experiencing the diverse effects of your sense of smell. Scents can become part of emotional memory, recreating certain responses to smells when you encounter them again in the future.
Not surprisingly, some scents are commonly associated with a more inviting bedroom environment. In the National Sleep Foundation’s 2012 Bedroom Poll, 78% of people said they were more excited for bed when their sheets had a fresh scent, and 71% of people described getting more comfortable sleep with fresh sheets.
Sheets, though, are just one source of bedtime fragrances, and there are indications that bringing other scents into the bedroom with aromatherapy may promote improved sleep.
Aromatherapy utilizes scents from plants to try to enhance different aspects of health. Forms of aromatherapy date back to ancient Egypt and are based on the use of essential oils, which are liquids made with materials extracted from plants like flowers or herbs.
There are three main ways that essential oils can be used for aromatherapy.
- The indirect inhalation method disperses the oil through a room, mixing it with the air so that each breath involves low concentrations of the scent. The oil can be spread with a device known as a diffuser or by applying it to an absorbent material like a tissue.
- The direct inhalation method involves breathing in air or vapor with a more concentrated level of compounds from the essential oil. In clinical research studies, this may be done with special nasal devices, but at home, most people put drops of essential oil onto hot water and inhale the vapor.
- The skin application method mixes an essential oil with a more neutral oil, known as a carrier oil, that is then rubbed or massaged onto the skin. This allows the smell to be perceived by the nose as well as by olfactory receptors in the skin. While much more has to be learned about the function of these receptors, they may provide another input to the body’s sensory system.
Can Aromatherapy Help With Sleep?
Evidence suggests that aromatherapy may be able to help with sleep by creating a bedroom environment that is more conducive to falling asleep and staying asleep.
Exposure to smells that are associated with a positive mood, calmness, and relaxation may be beneficial in the lead-up to bedtime and through the night. Stress and anxiety, forms of mental hyperarousal, frequently contribute to sleeping problems like insomnia.
By promoting relaxation, certain essential oils may reduce this barrier to sleep. A review of published scientific research found that a majority of studies reported sleep benefits for people using essential oils. In a study in people with post-traumatic stress disorder (PTSD), a condition often marked by nightmares and significant sleeping problems, exposure to pleasant odors during sleep was associated with improved sleep quality.
While promising research supports the potential of aromatherapy to improve sleep, more rigorous research is needed before it can be considered a standard treatment for insomnia or other sleep disturbances. Some challenges to aromatherapy research include:
- The ease of detecting a fragrance makes it difficult to use a placebo to conduct blinded and randomized studies that would carry greater scientific weight.
- Many existing trials of aromatherapy deliver scents directly to the nose during sleep via a hose or special nasal applicator. Even if these studies show benefits, it is not known if other aromatherapy methods, such as indirect inhalation, generate the same results.
- There are many different formulations of essential oils, and the chemical composition of essential oils used in research studies may vary from those available to the general public.
Are There Side Effects to Aromatherapy?
Most studies report few or no side effects from aromatherapy, and essential oils are generally considered to be safe when used as directed.
Some people may experience allergic reactions to certain essential oils, especially those that are applied to the skin. Citrus-based and some other types of essential oils may increase the skin’s sensitivity to the sun and ultraviolet rays.
Tea tree and lavender essential oils have been found to contain chemicals that can be endocrine disruptors, meaning that they affect the production of sex hormones like androgens and estrogen. Studies have found that in rare cases, these oils are linked to prepubescent breast growth in girls and abnormal breast development in boys. The compounds believed to cause endocrine disruption have been found in at least 65 other types of essential oils. More studies are needed to define the potential risks of endocrine disruption from essential oils and how they may be avoided or reduced.
What Are the Best Scents for Sleep?
There is no consensus about the best types of aromatherapy for sleep. What works best for any individual may depend on the nature of their sleeping problems and their fragrance preferences.
The following sections describe essential oils that have shown benefits for sleep in research studies; however, it is important to remember that much of this research is preliminary or conducted in specific patient populations that may not be generalizable to the public as a whole.
Anyone with sleeping problems should talk with a doctor, and unless directed by a health professional, aromatherapy should not replace other treatments for insomnia or sleep disorders.
Among essential oils, few have been studied as much as lavender. Lavender has been associated with improved sleep in multiple research studies, including in some people with insomnia. The smell of lavender has calming effects on heart rate and blood pressure as well as mood. In a study of people exposed to lavender before bed, deep sleep increased, leading to feeling more refreshed in the morning.
Roses have a reputation for their appealing fragrance, and rose essential oils have shown potential as aromatherapy for sleep. While not conclusive, a study in depressed patients showed some indicators of enhanced mood and sleep when they inhaled rose-scented air during sleep.
In a study conducted in a hospital’s coronary care unit, aromatherapy with scents from a type of rose known as damask rose (rosa damascene) showed significant improvement in sleep quality.
In one study, roman chamomile essential oil applied to pillows improved total sleep time for older adults in managed care settings. In a separate study in cancer patients, massages given with a carrier oil blended with roman chamomile essential oil reduced patients’ self-reported levels of anxiety.
Jasmine essential oil that was dispersed in a bedroom during sleep was found to improve sleep efficiency, meaning that more of the time a person was in bed was actually spent sleeping.
Though not studied as extensively, a study using the scent of cedar extract helped people fall asleep more quickly when taking a nap during the daytime.
A preliminary study with cannabis essential oil made from plants that do not contain THC, the compound most responsible for the high associated with cannabis, found improved relaxation among people who inhaled this scent.
Ylang-ylang essential oil, derived from the Cananga tree, has been associated with calmness and slowed reaction times, which may make it helpful in the lead-up to sleep.
What Are the Best Scents To Wake You Up?
As with aromatherapy for sleep, there’s no guaranteed scent that will make everyone feel alert, but research has highlighted a few fragrances that may be beneficial.
Drinking coffee is one of the most popular pick-me-ups, but not everyone likes the flavor or wants to consume caffeine. Another option may be just smelling coffee without drinking it; a research study found that breathing in the smell of coffee improved alertness, attention, and memory without the physical effects of caffeine.
Rosemary essential oil has been found to be a stimulant that helps activate the brain and may promote alertness and overall cognition.
Peppermint essential oil has a distinct smell and in some research has boosted memory recall and feelings of alertness.
Preliminary research with essential oils from common sage (Salvia officinalis) and Spanish sage (Salvia lavandulifolia) have found both to be associated with enhanced mental performance.
Some types of blended essential oils may help with focus and attention. In one study, a blended oil with primary chemical components of 1,8-cineole, 3-carene, β-pinene, and β-caryophyllene improved cognitive performance and focus.
How Does Sleep Affect Your Sense of Smell?
As anyone with a stuffy nose can tell you, the strength of our sense of smell is not always the same. One factor that influences the olfactory system is your circadian rhythm. This part of our biological clock is known for how it promotes sleeping during the night and wakefulness during the day, but it affects numerous other bodily processes as well.
Researchers found that smell sensitivity changes through the day in accordance with our circadian timing. In general, sense of smell is the strongest in the evening (around 9:00 p.m.) and weakest overnight and into the wee hours of the morning. This reduction in smell sensitivity through the night may explain why odors generally don’t cause people to wake up from sleep.
Can Smells Affect Dreams?
Research has found that external stimuli during sleep, including smells, can affect dreams, but the nature of this effect remains unclear. In one study, positively associated smells promoted more positive dreams while unpleasant smells increased negative dreams. Other research, though, found the opposite, with exposure to a familiar odor or a preferred fragrance causing more negative dreams.
Many factors can influence dreams, and additional investigation is needed before it’s clear if and how aromatherapy can be used to affect dreams.
Can Smell During Sleep Improve Memory?
Memories are strengthened during sleep, which is part of why it’s important for learning. Sleep scientists have explored ways to reinforce this memory consolidation process, including exposure to smells during sleep.
The focus of this learning technique is to use odors as a memory cue. To accomplish this, a person is exposed to a specific fragrance while awake and learning new information. Then, they are exposed to that same fragrance during sleep. In a study of school children, memory recall on a vocabulary test was improved by this odor-based cueing. Additional benefits may come from being exposed to that same smell during testing the next day as well.
While this method does not eliminate the hard work of having to learn new material, it may benefit students and others who want to boost their chances of building useful memory during sleep.
Can Smell Help You Feel More Awake in the Morning?
While many people are intrigued by aromatherapy to help them sleep, others want to know how to harness smells to feel more alert in the morning.
Getting good sleep is your best bet for waking up refreshed and ready to go, and aromatherapy won’t make up for insufficient sleep. That said, some smells may increase your attention and energy in the morning or through the day.
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