Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are not contagious or life-threatening, but can be very uncomfortable. Contact dermatitis results from either exposure to allergens (allergic contact dermatitis), or irritants (irritant contact dermatitis). Allergic contact dermatitis involves a delayed type of hypersensitivity and previous exposure to an allergen to produce a reaction. Irritant contact dermatitis is the most common type and represents 80% of all cases. It is caused by prolonged exposure to irritants, leading to direct injury of the epidermal cells of the skin, which activates an immune response, resulting in an inflammatory cutaneous reaction. Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight. Diagnosis of allergic contact dermatitis can often be supported by patch testing. Epidemiology
Contact dermatitis constitutes 95% of all occupational skin disorders. There are few accurate statistics on the incidence and prevalence of contact dermatitis. The results of the few studies that have been undertaken cannot be compared because of methodological differences. Signs and symptoms
Contact dermatitis is a localized rash or irritation of the skin caused by contact with a foreign substance. Only the superficial regions of the skin are affected in contact dermatitis.
In a 2002 study involving 78 patients with a migraine or tension-type headache, CT scans showed abnormalities in over a third of the patients, though arachnoid cysts only accounted for 2.6% of patients in this study. A study found 18% of patients with intracranial arachnoid cysts had non-specific headaches. The cyst was in the temporal location in 75% of these cases. Seizures
Hydrocephalus (excessive accumulation of cerebrospinal fluid)
Increased intracranial pressure
Developmental delay
Behavioral changes
Nausea
Dysdiadokinesis
Hemiparesis (weakness or paralysis on one side of the body)
Ataxia (lack of muscle control)
Musical hallucination
Pre-senile dementia, a condition often associated with Alzheimers disease
In elderly patients (>80 years old) symptoms were similar to chronic subdural hematoma or normal pressure hydrocephalus:Dementia
Urinary incontinence
Hemiparesis
Headache
Seizures

Location-specific symptoms
A supratentorial arachnoid cyst can mimic a Ménières disease attack. Frontal arachnoid cysts have been associated with depression. Cysts on the left temporal lobe have been associated with psychosis. A left fronto-temporal cyst showed symptoms of alexithymia. Cyst on the right sylvian fissure resulted in new onset of schizophrenia-like symptoms at age 61. A patient with a cyst on the left middle cranial fossa had auditory hallucinations, migraine-like headaches, and periodic paranoia
Patients with left temporal lobe cysts had mood disturbances similar to manic depression (bipolar disorder) and were known to show outward aggression

Causes
The exact cause of arachnoid cysts is not known. Researchers believe that most cases of arachnoid cysts are developmental malformations that arise from the unexplained splitting or tearing of the arachnoid membrane.In some cases, arachnoid cysts occurring in the middle fossa are accompanied by underdevelopment (hypoplasia) or compression of the temporal lobe.