Self-stimulatory behavior, also known as "stimming" and self-stimulation, is the repetition of physical movements, sounds, words, moving objects, or other behaviors. Such behaviors (also scientifically known as "stereotypies") are found to some degree in all people, especially those with developmental disabilities such as attention deficit hyperactivity disorder (ADHD) and autism. People diagnosed with sensory processing disorder are also known to potentially exhibit stimming behaviors. Stimming has been interpreted as a protective response to overstimulation, in which people calm themselves by blocking less predictable environmental stimuli, to which they have a heightened sensitivity. A further explanation views stimming as a way to relieve anxiety and other negative or heightened emotions. Although some forms of stimming behaviors have typically been shown to be healthy and beneficial—as they help regulate intense sensory experiences and emotions— stimming is often socially stigmatized and looked down upon. People who are neurodivergent often feel that they need to hide or decrease their self-stimulatory behavior, as it appears to not be socially acceptable, and often elicits an undesirable response from those who do not understand the compulsion behind them. There are also potential mental health and well-being risks in suppressing and masking some autistic stimming behaviors that are harmless or generally adaptive. Stimming behaviors can consist of tactile, visual, auditory, vocal, proprioceptive (which pertains to limb sensing), olfactory, and vestibular stimming (which pertains to balance). Some common examples of stimming (sometimes called stims ) include hand flapping, clapping, rocking, blinking, pacing, head banging, repeating noises or words, snapping fingers, occasional toe walking, or spinning objects. In some cases, stimming may be dangerous and physically harmful to the person doing it; for example, individuals may risk injuring themselves by forcefully banging their body parts against walls. Another issue is that repetitive behaviors may disrupt learning for some autistic individuals in some situations.

Stimming and autism

Stimming behavior is almost always present in autistic people, but does not, on its own, necessarily indicate the diagnosis. The biggest difference between autistic and non-autistic stimming is the type of stim and the quantity of stimming. In the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association, stimming behavior is described as "stereotyped or repetitive motor mannerisms" and listed as one of the five key diagnostic criteria of autism spectrum disorder. Different perspectives suggest that stimming involves both sensory and motor functions. Underdevelopment of these sensorimotor functions can result in stimming behaviors produced by the person as a controllable response. One study which interviewed thirty-two autistic adults found that unpredictable and overwhelming environments caused stimming. Stimming can sometimes be self-injurious, such as when it involves head-banging, hand-biting, excessive self-rubbing, and scratching the skin. As it serves the purpose of self-regulation and is mostly done subconsciously, stimming is difficult to suppress. Managing the sensory and emotional environment while increasing the amount of daily exercise can increase comfort levels for the person, which may reduce the amount of the need for stimming. Consciously or subconsciously suppressing stimming with the aim to present as neurotypical is one type of autistic masking. It typically requires an exceptional effort and can negatively impact mental health and well-being.

Stimming and ADHD

Stimming is practiced by some, but not all, people with ADHD. The cause is not thoroughly understood, but experts believe stimming is likely linked to the effects of the dopamine imbalance that occurs in the brains of people with ADHD. Some of the reasons people with ADHD might stim include to help them focus, to process and deal with their emotions, to help to deal with boredom, to express excitement, to cope with being overwhelmed by their environment, and to help them concentrate when they are uninterested with a topic or task. The behaviors associated with ADHD stimming are characteristically repetitive and can be done consciously or unconsciously. Many neurotypical people may exhibit the same stimming behaviors, referred to as fidgeting, as someone with ADHD. However, for people with ADHD, these behaviors are more severe, occur more often, and can affect the person’s daily lives. Some potentially more negative or harmful stimming behaviors include teeth grinding, biting one's fingernails and lips, picking at one’s skin and scabs, overeating, impulsive actions, and chewing the inside of the cheeks. For people with ADHD, stimming can change over time. Some stims may lessen or disappear over time, while other stims can emerge as the result of other stressors. ADHD symptoms can be aggravated by certain environments, situations, and emotions, which will trigger stimming behavior. Some of these triggers include situations involving certain emotions like conflict and rejection, distractions caused by television and phones, environments that are messy or busy, strong or distracting odors, and intense lighting.

Toys

Small objects known as stim toys or sensory toys may be used to satisfy a person's stimming behaviours. A stim toy may be specially designed for a specific stimming behaviour, such as a fidget toy, or it may be any ordinary object that a person can manipulate to perform the desired stimming behaviour. Many popular stim toys are held in the hands; they may also provide oral stimulation, such as chewelry.