Pepper spray in the context of Capsaicin

Riot control is a form of public order policing used by law enforcement, military, paramilitary or security forces to control, disperse, or arrest people who are involved in a riot, demonstration or protest.

If a riot is spontaneous, then actions which cause people to stop and think (e.g. loud noises or issuing instructions in a calm tone) can be enough to stop it. However, these methods usually fail when there is severe anger, or the riot was planned or organized. Riot control personnel have long used less lethal weapons such as batons and whips to disperse crowds and detain rioters. Since the 1980s, riot control officers have also used tear gas, pepper spray, rubber bullets, stun grenades, and electric tasers. In some cases, riot squads may also use Long Range Acoustic Devices, water cannons, armoured fighting vehicles, aerial surveillance, police dogs or mounted police on horses. Persons performing riot control typically wear protective equipment such as riot helmets, face visors, body armor (vests, neck protectors, knee pads, etc.), gas masks and riot shields. Even though riot tactics are effective in controlling crowds, they can also lead to significant psychological effects on both the rioters and the police. Exposure to intense fear, stress, and violence during these confrontations can result in long-term mental health issues, like anxiety, post-traumatic stress disorder (PTSD), and heightened aggression, which can impact the well-being of protesters and police officers.

Tear gas, also known as a lachrymatory agent or lachrymator (from Latin lacrima 'tear'), sometimes colloquially known as "mace" after the early commercial self-defense spray, is a chemical weapon that stimulates the nerves of the lacrimal gland in the eye to produce tears. In addition, it can cause severe eye and respiratory pain, skin irritation, bleeding, and blindness. Common lachrymators both currently and formerly used as tear gas include pepper spray (OC gas), PAVA spray (nonivamide), CS gas, CR gas, CN gas (phenacyl chloride), bromoacetone, xylyl bromide, chloropicrin (PS gas) and Mace (a branded mixture).

While lachrymatory agents are commonly deployed for riot control by law enforcement and military personnel, its use in warfare is prohibited by various international treaties. During World War I, increasingly toxic and deadly lachrymatory agents were used.

Non-lethal weapons, also called nonlethal weapons, less-lethal weapons, less-than-lethal weapons, non-deadly weapons, compliance weapons, or pain-inducing weapons are weapons intended to be less likely to kill a living target than conventional weapons such as knives and firearms with metal-projectile ammunition. It is often understood that unintended or incidental casualties are risked wherever force is applied; however, non-lethal weapons minimise the risk of casualties (e.g. serious/permanent injuries or death) as much as possible. Non-lethal weapons are used in policing and combat situations to limit the escalation of conflict where employment of lethal force is prohibited or undesirable, where rules of engagement require minimum casualties, or where policy restricts the use of conventional force. However, these weapons occasionally cause serious injuries or death due to allergic reactions, improper use and/or other factors; for this reason the term "less-lethal" has been preferred by some organizations as it describes the risks of death more accurately than the term "non-lethal", which some have argued is a misnomer.

Non-lethal weapons may be used by conventional military in a range of missions across the force continuum. They may also be used by military police, by United Nations forces, and by occupation forces for peacekeeping and stability operations. Non-lethal weapons may also be used to channelize a battlefield, control the movement of civilian populations, or to limit civilian access to restricted areas (as they were utilized by the USMC's 1st Marine Expeditionary Force in Somalia in 1995). Similar weapons, tactics, techniques and procedures are employed by police forces domestically in riot control, prisoner control, crowd control, refugee control, and self-defense, where the terminology of "less-than-lethal" is often used.

A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a weapon "or its precursor that can cause death, injury, temporary incapacitation or sensory irritation through its chemical action. Munitions or other delivery devices designed to deliver chemical weapons, whether filled or unfilled, are also considered weapons themselves."

Chemical weapons are classified as weapons of mass destruction (WMD), though they are distinct from nuclear weapons, biological weapons, and radiological weapons. All may be used in warfare and are known by the military acronym NBC (for nuclear, biological, and chemical warfare). Weapons of mass destruction are distinct from conventional weapons, which are primarily effective due to their explosive, kinetic, or incendiary potential. Chemical weapons can be widely dispersed in gas, liquid and solid forms, and may easily afflict others than the intended targets. Nerve gas, tear gas, and pepper spray are three modern examples of chemical weapons.

A black bloc (sometimes black block) is a tactic used by protesters who wear black clothing, ski masks, scarves, sunglasses, motorcycle helmets with padding, or other face-concealing and face-protecting items. The clothing is used to conceal wearers' identities from both the police and politically opposing organizations by making it difficult to distinguish between participants. It is also used to protect their faces and eyes from pepper spray, which is used by police during protests or civil unrest. The tactic also allows the group to appear as one large unified mass. Black bloc participants are often associated with anarchism, anarcho-communism, communism, libertarian socialism and proletarian internationalism. A variant of this type of protest is the Padded bloc, where following the Tute Bianche movement protesters wear padded clothing to protect against the police.

The tactic was developed in the 1980s in the European autonomist movement's protests against squatter evictions, nuclear power, and restrictions on abortion, as well as other influences. Black blocs gained broader media attention outside Europe during the 1999 Seattle WTO protests, when a black bloc damaged property of Gap, Starbucks, Old Navy, and other multinational retail locations in downtown Seattle.

Mace is the brand name of an early type of aerosol self-defense spray invented by Alan Lee Litman in the 1960s. The first commercial product of its type, Litman's design packaged phenacyl chloride (CN) tear gas dissolved in hydrocarbon solvents into a small aerosol spray can, usable in many environments and strong enough to act as a deterrent and incapacitant when sprayed in the face.

A generic trademark, its popularity led to the name "mace" being commonly used for other defense sprays regardless of their composition, and for the term "maced" to be used to reference being pepper sprayed. It is unrelated to the spice mace.

PAVA spray is an incapacitant spray similar to pepper spray. It is dispensed from a handheld canister, in a liquid stream. It contains a 0.3% solution of pelargonic acid vanillylamide (PAVA), also called nonivamide, a synthetic capsaicinoid (analogue of capsaicin), in a solvent of aqueous ethanol. The propellant is nitrogen. This solution has been selected because this is the minimum concentration which will fulfill the purpose of the equipment: namely, to minimise a person's capacity for resistance, without unnecessarily prolonging their discomfort.

PAVA is significantly more potent than CS gas. The liquid stream is a spray pattern and has a maximum effective range of up to four metres (13 ft). Maximum accuracy, however, will be achieved over a distance of 1.25–2 metres (4.1–6.6 ft). The operating distance is the distance between the canister and the subject's eyes, not the distance between the user and the subject.

The inorganic dye ammoniated ruthenium oxychloride, also known as ruthenium red, is used in histology to stain aldehyde fixed mucopolysaccharides.

Ruthenium red (RR) has also been used as a pharmacological tool to study specific cellular mechanisms. Selectivity is a significant issue in such studies as RR is known to interact with many proteins. These include mammalian ion channels (CatSper1, TASK, RyR1, RyR2, RyR3, TRPM6, TRPM8, TRPV1, TRPV2, TRPV3, TRPV4, TRPV5, TRPV6, TRPA1, mCa1, mCa2, CALHM1) TRPP3, a plant ion channel, Ca-ATPase, mitochondrial Ca uniporter, tubulin, myosin light-chain phosphatase, and Ca binding proteins such as calmodulin. Ruthenium red displays nanomolar potency against several of its binding partners (e.g. TRPV4, ryanodine receptors,...). For example, it is a potent inhibitor of intracellular calcium release by ryanodine receptors (Kd ~20 nM). As a TRPA1 blocker, it assists in reducing the airway inflammation caused by pepper spray.