The goal of this observational study is to learn how stress affects children and young people with autism spectrum disorder (ASD). Many individuals with autism experience strong stress reactions that may lead to challenging behaviours such as agitation, withdrawal, aggression, or self-injury. These behaviours can be difficult to predict, especially in people who have limited communication abilities.

Researchers want to better understand how the body reacts to stress in real-life situations. The study focuses on two main biological systems involved in the stress response:

the autonomic nervous system, which produces fast reactions such as changes in heart rate and sweating, and the hypothalamic-pituitary-adrenal axis, which produces slower hormonal responses such as cortisol.

The main questions the study aims to answer are:

• Do physiological stress signals differ between individuals with ASD and those without ASD?
• Are there differences in physiological stress responses between individuals with ASD and non-ASD participants?
• Can physiological markers help identify stress earlier in people with autism?

Researchers will compare children and young people with autism to a control group of participants without autism to see whether their stress responses differ.

Participants will take part in monitoring during their normal daily activities. This allows researchers to observe stress responses in natural environments such as school, home, or specialized care institutions.

Participants will:

• Wear a wrist device during the day that measures heart rate, heart rate variability, skin conductance, skin temperature, and movement
• Provide saliva samples in the morning and afternoon to measure stress hormones such as cortisol and alpha-amylase
• Have additional saliva samples collected after behavioural crises or stressful events when possible
• Be observed by a trained researcher who records behavioural events and the surrounding context

Researchers will combine physiological data, behavioural observations, and contextual information such as physical activity, environmental conditions, and daily routines. This will help identify patterns of stress in everyday life.

The results of this study may help researchers better understand the physiology of stress in autism and support the future development of wearable systems that could detect stress early and help prevent behavioural crises.

1. Autism Spectrum Disorder (ASD) Group Inclusion Criteria

   • Age between 3 and 22 years
   • Clinical diagnosis of autism spectrum disorder according to established diagnostic criteria
   • Presence of recurrent behavioral crises (minimum of three episodes per week)
   • Enrollment in a participating institution or care structure
   • Written informed consent provided by a parent or legal guardian
   • Assent from the participant when developmentally appropriate

   Exclusion Criteria:

   • Known cardiac or homonal disorders that may interfere with physiological monitoring
   • Lack of consent from parents or legal guardians

2. Control Group (Neurotypical Participants) Inclusion Criteria

   • Age between 3 and 22 years
   • No diagnosis of autism spectrum disorder or other neurodevelopmental disorder
   • No history of major psychiatric or neurological disorders
   • Written informed consent provided by a parent or legal guardian
   • Assent from the participant when developmentally appropriate

Exclusion Criteria

• Known cardiac or hormonal disorders affecting physiological measurements
• Current diagnosis of neurodevelopmental or psychiatric disorder
• Lack of parental or guardian consent

The study population consists of children and adolescents aged 3 to 22 years. Two groups are included: individuals diagnosed with autism spectrum disorder (ASD) presenting recurrent behavioral crises, and a neurotypical control group without neurodevelopmental disorders. Participants with ASD are recruited from specialized medico-social institutions providing care and educational support for individuals with neurodevelopmental conditions. Control participants are recruited from the general population through community outreach and school-based information to families.

Participants are observed during their regular daily activities in naturalistic environments such as specialized institutions, schools, or home settings. Continuous physiological monitoring, behavioral observation, and biological sampling are conducted during daytime institutional sessions.