"You should smile more": Population-level sex differences in smiling also exist in autistic people.
Casey J Zampella, Julia Parish-Morris, Jessica Foy and 3 others
PMID 39560147WHAT IT FOUND
Autistic girls and women smiled more than autistic boys and men, looking more like neurotypical boys than neurotypical girls.
This sex-based difference persisted in autism, meaning autistic females may present with fewer obvious social traits and risk being missed by standard male-referenced assessments.
Key findings
01Female participants smiled more than male participants, and neurotypical participants smiled more than autistic participants, with no interaction between diagnosis and sex.
02Autistic females exhibited smile activity most comparable to neurotypical males, rather than neurotypical females.
03Conversation partners rated females and neurotypical participants higher on interaction quality, mirroring the smiling patterns.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The sample was limited to verbally fluent individuals with IQs above 75, so results do not apply to non-speaking or intellectually disabled autistic people. Sex was classified as binary based on parent-reported natal sex, excluding non-binary or transgender identities. Conversation partners were primarily female volunteers in their early twenties, which may have influenced interaction dynamics and ratings. The study did not measure internal emotional states, so it cannot confirm whether increased smiling in females reflects genuine positive affect or social compliance. The relationship between smiling and social impressions in autistic males was not statistically significant and should be interpreted with caution.
Declared interests
The authors declared no conflicts of interest. The study was supported by NIH grants.
The easy way to misread this
Do not assume that autistic females are 'less autistic' than males. They smiled more than autistic males, but still less than neurotypical females, indicating a distinct profile rather than a milder presentation. Standard assessments may miss them because their overt behavior aligns more with female social norms than with the male-referenced autism prototype.