Past research has looked extensively at how autism spectrum disorder (ASD) impacts sensory functioning, such as vision, touch, and sound. For example, it is well known that children who have autism are not naturally oriented toward social sounds and that this is a factor in the deficits they have in social engagement.
But there has not been as much research on the connection between the sense of smell, or olfaction, and autism. Anecdotal documentation and experimental research have shown the importance of odor cues in a child’s environment for their social and cognitive development.
What little research there has been hasn’t received the attention it should. Understanding the link between the sense of smell and autism can help parents better support their children if they do react more to scents. Learn more about this unique connection.
Scent & Autism Spectrum Disorder
Scent is so important for children with autism because ASD leads to deficits in social communication, behavior, and interaction, as well as atypical sensory behavior and responses. Both dimensions are closely linked.
The available research suggests that children with autism have atypical responses to olfactory stimuli, similar to how other children with ASD might react atypically to taste or tactile stimuli.
The Functions of Olfaction
Children with autism use different regions of their brain to tell apart the smells of people they know and people they don’t know, compared to neurotypical people. One study found that adult men with autism reacted differently when they smelled sweat from skydivers, compared to neurotypical men who also smelled sweat from skydivers.
Because no one is regularly sniffing skydivers, what exactly does this mean for your child? Some children with autism will be more sensitive to certain smells than others. They may even inhale differently than other people.
The reason for all this is that olfaction, or the sense of smell, has vital functions. Being able to smell is critical for ingestive behaviors (such as eating and drinking), awareness of environmental dangers (for example, the olfactory sense is a form of an early warning system, being able to detect bad smells to protect against eating toxic food), and even social communication. In 2021, the Cell and Tissue Research journal noted that the olfactory system can regulate emotional conditions across life, from prenatal stages to selecting an intimate partner.
However, these functions have not been fully studied in people (and especially children) who have autism. In a 2015 experiment, researchers discovered that while neurotypical children had a sniff response akin to adults within 300 milliseconds of an odor being released, children with autism “had a profoundly altered sniff response,” sniffing regardless of the strength or the nature of the smell. Children with more severe forms of autism (especially those who had more social impairments) displayed greater degrees of aberrant sniffing.
The mechanism to test this was a nasal cannula, a small tube that sends odors directly into the nose and measures nasal airflow. The device can deliver typically pleasant fragrances or unpleasant smells.
The researchers concluded that “aberrant sniffing” was an important mechanistic link between scent and smelling, autism spectrum disorder, and impaired social behavior and abilities.
Scent & Social Impairment
Studies on the importance of scent for children with autism suggest that smell is hindered in children who have autism. The different responses to the nature and source of smells are a function of their social impairment.
When most people encounter a pleasing smell, they tend to inhale deeply. Conversely, the smelling is more tentative for smells that can be considered foul.
Children with autism tended to buck that dynamic and sniffed with the same intensity for each type of odor. And the less a child’s sniff response varied between pleasant and unpleasant odors, the greater likelihood that the child had more severe social deficits.
Researchers hope that since the sniff test does not require speech, it can be a tool in autism diagnosis for toddlers who are not yet verbal. Another benefit of the sniff test is that it does not require children to pay attention or follow directions. In the study, the children were shown cartoons while being administered the smells, so the researchers could study how the children responded to smells even when their attention was focused elsewhere.
Other researchers expressed interest in the fact that while children with autism exhibit hypersensitivity to other stimuli (such as taste, touch, and sound), they do not respond to odor in the same way. This might prove notable for better understanding the social difficulties children with autism experience in ways the traditional understandings of hypersensitivity have not been able to shed light on.
Aromatherapy as Treatment
Frontiers in Psychology explains that for children who have autism, all smells and odors are alerting. This becomes essential in providing a sensory-enriching home environment for children past the toddler stage. There might be some trial and error in finding scents that your child finds comforting or that they associate with positive activities.
Aromatherapy research has found that rose, lavender, and vanilla scents are calming, while mint, citrus, and cinnamon are invigorating.
Children with autism sometimes demonstrate a need to smell everything to add to their sensory input. This is theorized to be associated with the need to gain more information through sensory channels with which they are more comfortable. This means that as much as you should provide a scent-sensitive home for your child, you should also make sure their other sensory systems receive similar input.
Some children with autism may seek out familiar smells to calm themselves when they are distressed or experiencing sensory overload. Observe what your child actively looks to smell or what smells are present to calm themselves down. You can adapt your home accordingly and share this information with your child’s Board-Certified Behavioral Analyst (BCBA) therapist.
Smell Training & Limitations
Some parents have turned to educational tools that combine reading with “smell training” for their autistic children. Forbes magazine profiled the development of a book that combines colors, smells, and emotional storytelling to help children with autism learn how to use sensory stimuli to understand the world around them and express their emotions clearly.
The book’s author explained that the brain’s limbic system, which regulates memory, odor, and emotion, is foundational for a child to process their environment. This develops prenatally in neurotypical children; in children who have autism, the development is slowed.
Educational materials, such as the book profiled by Forbes, help introduce and establish connections between smell and other environmental cues that do not come naturally to children with autism. This plays a vital role in helping them build their emotional communication and development.
Aromatherapy is not an end-all for helping children with autism, and it should not be used as such. One study, published in Evidence-Based Complementary and Alternative Medicine, found no notable differences in sleep between nights in which the children in the study (who had autism) received aromatherapy treatments and the nights in which they didn’t. The researchers concluded that longer-term interventions might have more impact than other sensory changes in the home environment.
Early Social Attention Impairments in Autism: Social Orienting, Joint Attention, and Attention to Distress. (March 2004). Developmental Psychology.
Men With Autism May Misread Social Cues in Body Odor. (December 2017). Scientific American.
Learning About the Functions of the Olfactory System From People Without a Sense of Smell. (March 2012). PLoS One.
The Importance of the Olfactory System in Human Well-Being, Through Nutrition and Social Behavior. (January 2012). Cell and Tissue Research.
A Mechanistic Link Between Olfaction and Autism Spectrum Disorder. (July 2015). Current Biology.
Classification of Children With Autism Spectrum Disorder By Sensory Subtype: A Case for Sensory-based Phenotypes. (June 2014). Autism Research.
Odor Perception in Children With Autism Spectrum Disorder and Its Relationship to Food Neophobia. (December 2015). Frontiers in Psychology.
How a Children’s Book Offers Scent as a Resource for Autistic Children. (October 2021). Forbes.
Evaluating Effects of Aromatherapy Massage on Sleep in Children With Autism: A Pilot Study. (April 2006). Evidence-Based Complementary and Alternative Medicine.