Sensory defensiveness
Sensory defensiveness is a condition defined as having "a tendency to react negatively or with alarm to sensory input which is generally considered harmless or non-irritating" to neurotypical persons.
It is not uncommon for individuals to have a few mild sensory defensive traits. However, when multiple defensive traits impact the person's day-to-day life, that person is considered to be Sensory Defensive.

# Symptoms
Common symptoms of sensory defensiveness include intolerance of high-pitched noises, intolerance of overhead lights (especially fluorescent lighting); experiencing a feeling of being attacked upon being touched (especially from light touch or sudden touch); intolerance of certain types of fabrics in contact with the skin; becoming nauseated upon smelling something that does not smell bad to normal individuals; difficulty maintaining eye-contact; severe intolerance of foods due to taste, texture, or temperature; and generally becoming overwhelmed when exposed to a lot of sensory stimuli at once.
Intolerance in this context should not always be taken as unwillingness to be subject to the sensory stimuli in question; rather, intolerance is an inability to process the sensory stimuli in any way other than as over-stimulating, because the sensory stimuli provokes a fight-or-flight reaction.  This is also known as sensory overload.
Sensory defensiveness can vary between individuals:
- The senses that are problematic for one person may not be so for another.  (Commonly, individuals report major issues with two or three senses and minor issues with the other senses.)
- How easily and the way in which a particular sense bothers individuals varies (e.g. high-pitched noises may annoy someone, or they may hurt his/her ears; touch may provoke anxiety, or it can be painful).
- The triggers for a particular sense vary between people (e.g. one person may be sensitive to the texture of mushy foods, while another may be sensitive to crunchy foods).

# Causes
There are believed to be multiple etiologies for sensory defensiveness, including genetic factors, environmental conditioning, drug or alcohol abuse, sexual abuse, or premature birth.  Those diagnosed with attention deficit hyperactivity disorder report much higher than average rates of hypersensitivity to sensory stimulus.

# Effects and treatment
Sensory overload can lead to what is commonly termed a "melt-down".  This may look much like a tantrum, or a person may undergo dissociation, which causes him/her to withdraw into himself/herself.  Individuals will often cope with their sensory difficulties by avoiding those situations that cause them irritation.  Occupational therapists often prescribe "sensory diets".  This is a therapy that is tailored to the individual in which he/she gets to experience calming sensory stimuli that help to balance his/her sensory system.  Snoezelen rooms, in which sensory experiences can be controlled and explored, are sometimes used.  Individuals will often naturally create or find their own calming sensory stimuli (stims) or sensory diets.
The other side to these issues is that many people report a positively heightened awareness of their senses, under the right conditions.  They also promote "stims", which can include music, exercise, and any other pleasing sensory stimulation, as natural means of reducing stress.

# Component of other disorders
Sensory defensiveness is a part of Sensory Integration Dysfunction.  Sensory Integration Dysfunction is considered a symptom of the autism spectrum, but a person does not have to display other autistic traits to have sensory defensiveness or sensory integration dysfunction.  Sensory integration dysfunction and defensiveness are also common with developmental dyspraxia, cerebral palsy, and fetal alcohol syndrome.