As published on Cell.com on July 20 of this year, researchers tested the sniff response in 36 children, 18 with autism spectrum disorder and 18 without, to see if the sniff response in children with autism is different than the neurotypical. To measure the sniff response, the researchers built a “computer-controlled air-dilution olfactometer equipped with a custom-designed double-barreled pediatric nasal cannula that allowed [the researchers] to simultaneously deliver odors and measure nasal airflow.” This instrument was used to measure the sniff response to “pleasant (rose or shampoo) and unpleasant (sour milk or rotten fish) odors.” The procedure took 10 minutes and consisted of 20 different smells (10 of each type) while the children watched a cartoon. The four parameters measured to quantify the sniff response were “sniff volume, peak airflow rate, mean airflow rate, and duration.” Note, the sniff response was not done in relation to any verbal cues or task.
Results of the study showed that children without autism spectrum disorder took “larger sniffs” for pleasant odors versus unpleasant odors. There was no difference in the sniffs between pleasant and unpleasant smells in the autism group. The researchers also found that the greater aberrant sniffing (non-adjustment of the sniff based on the properties of the odor), the more severe the autism. The difference in the two groups persisted even with “equal reported odor perception” (children identified equally between the two groups whether smell was supposed to be pleasant or unpleasant).
I would caution on extrapolating too much from the study regarding aberrant sniffing as the sample size is small. Also, from personal experience, the intensity of the smell, irrespective of whether the particular smell is deemed “pleasant” or “unpleasant” makes a big difference as to how I (who am on the autism spectrum) react to the smell. For example, I cannot stand intense perfume smells that emanate from a person or a cleaning product regardless of whether the actual smell is something pleasant like a flower.