Sensory processing disorder (SPD) is a neurological condition that interferes with the body’s ability to receive messages from the senses and convert them into correct motor and behavioral responses. It inhibits a person’s ability to filter out unimportant sensory information, making them feel overwhelmed and over-stimulated in crowded, smelly, noisy environments. A person with SPD may also find it difficult to process and act on information received by sight, sound, touch, smell, and taste. The condition may manifest as slowness performing or learning tasks at school, clumsiness or messy handwriting, sensitivity to certain sensations, or a tendency to seek excess stimulation in roughhousing or moving fast.

Some experts believe that Sensory processing goes awry in as many as 10 percent of children. People with ADHD, autism spectrum disorders, and fragile X syndrome are much more likely to develop SPD. The condition is more commonly diagnosed in childhood, but some adults live undiagnosed for years, experiencing lifelong trouble at work, in relationships, and in social settings. Many people occasionally feel overwhelmed by too-loud noises or too-bright lights, but for children and adults with SPD, these sensations disrupt and overwhelm everyday life.

For some people, only one sense is affected, while others experience sensitivity across a combination of senses. Other people with SPD feel as if a shade has been pulled over the world, like they have muted sensory receptors. For these suffers, motor skills and posture can be affected. As with many neurological conditions, the singular cause of the condition is unknown, though scientists believe there is a genetic, hereditary component. However, certain factors may put children at higher risk, including:

• Maternal deprivation

• Premature birth

• Prenatal malnutrition

• Early institutional care

The three major categories of SPD include:

• Sensory Modulation Disorder

• Sensory Discrimination Disorder

• Sensory-Based Motor Disorder

Sensory modulation disorder is the most common form of SPD. It indicates trouble regulating responses to stimulation. People with it are under or over responsive, since the nervous system does not know when to pay attention to or ignore stimuli. It leads to abnormal sensory seeking, or hiding from stimulation.

People with sensory discrimination disorder feel confusion about the sources of sensations. This can lead to trouble knowing where you are in space, clumsiness, trouble noticing hunger, or difficulty discriminating between letters and the sources of sounds.

Sensory-based motor disorder leads to trouble with tasks that require motor control like holding utensils, sitting up straight, and balancing. People with sensory processing disorder may have trouble with one or all of the categories in different severity.

A widely varying severity of symptoms can make SPD difficult to diagnose. Left untreated, SPD can lead to constant feelings of overwhelm that can make sufferers isolate themselves to avoid over-stimulation. It can also lead to anxiety, secondary depression, social isolation, or trouble succeeding at school or work. Learn more about the symptoms — and how to get a diagnosis — here.