According to OSHA (Appendix A 29 CFR 1910.1200), the Hazard Communication Standard as: A chemical, which is not corrosive, but which causes a reversible inflammatory effect on living tissue by chemical action at the site of contact. A chemical is a skin irritant if, when tested on the intact skin of albino rabbits by the methods of 16 CFR 1500.41 for four hours exposure or by other appropriate techniques, it results in an empirical score of five or more. A chemical is an eye irritant if so determined under the procedure listed in 16 CFR 1500.42 or other appropriate techniques”. A more general definition is a substance which on immediate, prolonged, or repeated contact with normal living tissue will induce a local inflammatory reaction. Additional Info: 16 CFR 1500.3 defines a primary irritant as a substance that is not corrosive and that human experience data indicate is a primary irritant and/or means a substance that results in an empirical score of five or more when tested by the method described in Sec. 1500.41. The effect of irritants is temporary. For example, pepper spray is a severe eye irritant, but causes no lasting effects. Chronic irritation should be discussed with your physician as it can be symptom of a variety of other underlying disease conditions or allergies. MSDS Relevance: It is sometimes difficult to tell whether an itch, redness or other irritation is the result of a chemical exposure. Be sure to wear personal protective equipment (PPE) (such as gloves, goggles, aprons or dust masks) that is effective for the kind of irritant you are working with. First aid treatment for skin irritation is to flush the affected area with water. Consult a physician if the symptoms persist or you have concerns about possible transdermal (through the skin) toxicity. The most effective first aid treatment for eye irritation caused by chemicals or foreign bodies in the eye is to flush the eyes with an ANSI-approved eye wash. Follow up with a physician, especially if a foreign body was involved (corneal abrasions or scratches are possible) or the chemical was basic (bases can cause severe eye damage even with water flushing). See also: Dermatitis, Inflammation, Sensitizer, Urticaria, Vesicant