Pepper spray, or Oleoresin Capsicum (OC) spray, is a lachrymatory agent -- a compound that makes the eyes tearful. The active ingredient in pepper spray is also an inflammatory agent that swells up the eyes and mucous membranes of the upper respiratory tract. It often causes pain and temporary blindness, while tear gas may cause permanent blindness.
It is used as self-defence against human and wild animal attack, as well as during riots and as a crowd-control device. Since 1973, pepper spray has been used by law enforcement as a way to subdue violent, aggressive or uncooperative subjects; it was used initially by the FBI and US police to incapacitate humans and animals temporarily.
The active ingredient in pepper spray is capsaicin, which is a chemical derived from the fruit of plants in the Capsicum genus, including chillies. Extraction of oleoresin capsicum from peppers requires capsicum to be finely grounded, from which capsaicin is then extracted using an organic solvent such as ethanol.
The solvent is then evaporated, and the remaining wax-like resin is the oleoresin capsicum. An emulsifier such as propylene glycol is used to suspend the OC in water, and pressurised to make it aerosol in pepper spray. The high performance of the liquid chromatography (HPLC) method is used to measure the amount of capsaicin and major capsaicinoids in pepper sprays.
The police use pepper spray so that they can restrain violent protesters, who become temporarily blinded, and so can be more easily removed from the scene.
Effects on the body
Skin: Skin exposure to pepper spray can cause intense pain, burning and even blistering of the skin. It worsens skin conditions like allergic dermatitis, and in severe cases, it can cause hypothermia.
Eyes: OC causes a burning pain in the eyes, inflammation and involuntary closing of the eyelids. In extreme cases it can cause temporary blindness. It can also cause longer-term eye damage because of sustained loss of blink reflex and/or anesthesia, which can cause corneal abrasions from contact lenses or other foreign material.
Respiratory System: Pepper spray often causes a burning throat, wheezing, gagging, and difficulty in breathing. In extreme cases, it can cause laryngospasm, which leads to an inability to speak or breathe. For those with asthma, exposure to OC can even cause death.
Some people can subsequently experience intense headaches for several hours.
Depending on the brand, pepper spray can contain water, alcohols, or organic solvents as a carrier for OC. They can also contain nitrogen, carbon dioxide, or halogenated hydrocarbons as propellants. Some of these chemicals can have serious cardiac, respiratory and neurologic, and teratogenic effects when inhaled in high doses.
Is mace better than pepper spray?
No. Mace is a tear gas, an irritant, while pepper spray is an inflammatory agent. Mace causes the eyes to tear up (permanent blindness) and stings the skin. Pepper spray causes temporary blindness and temporary breathing difficulties.
Legality
Pepper spray is banned for use in war by Article I.5 of the Chemical Weapons Convention, which bans the use of all riot control agents in warfare, whether lethal or less-than-lethal.
What to do if sprayed with pepper spray?
Remove as much spray as possible. Peel off your shirt or other clothing if it is contaminated with pepper spray. The idea is to eliminate as much contact as possible with your skin, and spray will seep through clothing.
Once your breathing is under control, use a washcloth dipped in cold, soapy water to wash yourself. Use soap liberally and rinse frequently by dousing the area with clean water. Don't wash with warm water as it may worsen the pain.
Stay away from hand lotions and any oil-based product that could seal over your skin and trap the pepper oils that are burning your body.
Don't rub or scratch
Pepper spray is made of oleoresin capsicum, an oil from chilli peppers that will smear all over your skin when rubbed, worsening your situation.
Though you may itch terribly, resist the temptation to scratch. Vigorous scratching can break the skin surface, allowing the pepper oils to seep under your skin. If you think it burns on the outside, you don't want to find out what it's like to have pepper spray in a cut or scratch.
Try some activity that distracts your mind from the pain as much as possible. Swimming in cold water may ease the irritation, but if that is not possible, try soaking in a tub while listening to quiet music. In about an hour, the worst of your symptoms should have subsided.
Persistent irritation, prolonged difficulty breathing, vision problems and any other medical concerns should be brought to the attention of a doctor.

The writer is in the Department of Psychiatry, Sylhet MAG Osmani Medical College and Hospital.