As combustion is an oxidation-reduction reaction, strong reducing agents tend to be very flammable. Since many of the strongest reducing agents react with water to generate products that are also flammable, water cannot be used to put out fires of strong reducing agents, especially metals. Members of this group are often included in explosive mixtures.

Strong reducing agents often react vigorously with other compounds, generating heat. Gaseous products may also be generated, which can pressurize a closed container, and which may go on to participate in further reactions. Oxygen, a moderately strong oxidizing agent, is ubiquitous in the atmosphere and can react rapidly with the compounds in this class. A dramatic example of an oxidation-reduction (or redox) reaction is the reaction of a piece of sodium metal with water. When sodium is dropped into water, the sodium is acting as a reducing agent and the water is acting as a (very weak) oxidizing agent. This reaction generates hydrogen gas as well as heat and sparks which can ignite the hydrogen and cause it to explode.

Reactions of strong reducing agents with compounds that are known oxidizing agents are often explosive. However, potentially explosive mixtures of oxidizing agents and reducing agents can persist unchanged for long periods if disturbances (heat, spark, catalyst, mechanical shock) are prevented. Another, more dangerous class of explosives are those where the oxidizing agent and reducing agent are actually different parts of the same compound. These compounds are generally much more sensitive than mixtures of separate oxidizing and reducing agents and may be used as detonators or primary explosives.

Most are toxic by ingestion; degree varies widely. Additionally, gaseous or liquid reducers may cause chemical burns if inhaled or if they come into contact with skin.

A reducing agent is a substance that usually reacts by adding electrons to other substances, a process known as reduction. The opposite process (removal of electrons from a compound) is known as oxidation and always occurs simultaneously with reduction. The overall reaction is termed an oxidation-reduction, or "redox", reaction.

There is a wide range of possible reducing strengths, and this reactivity group is intended to cover those reducers that are strong enough to react vigorously with water or oxygen under ambient conditions and are not already covered in other reactive groups. Some of the strongest reducing agents are categorized in other groups, including Metal Hydrides, Metal Alkyls, Metal Aryls, and Silanes; Chlorosilanes; Sulfides, Inorganic; Nitrides, Phosphides, Carbides, and Silicides; Metals, Alkali, Very Active; and Metals, Elemental and Powder, Active.

Compounds that contain both an oxidizing component and a reducing component (such compounds are often explosives) are classified in both an Oxidizing Agent reactive group and a Reducing Agent reactive group.

Ammonium hypophosphite, arsine, decaborane, hypophosphorous acid, phosphine, phosphorus trichloride, phosphorus, stibine, titanium trichloride.