As combustion is an oxidation-reduction reaction, many weak reducing agents are flammable or combustible. However, weak reducing agents may require forcing conditions, such as high temperatures and pressures, in order to burn.

Weak reducing agents will react less vigorously than a strong reducing agent, but can still participate in reactions that generate heat and possibly gaseous products 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 with the compounds in this class.

Reactions of weak reducing agents with compounds that are known oxidizing agents may result in combustion and can potentially be explosive if the mixture is heated or under pressure. Additionally, potentially explosive mixtures of oxidizing agents and reducing agents can persist unchanged for long periods if disturbances (heat, spark, catalyst, mechanical shock) are prevented.

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 are not strong enough to react vigorously with water or oxygen under ambient conditions and are not already covered in other reactive groups. Some weak reducing agents are categorized in other groups, including Organometallics; Sulfite and Thiosulfate Salts; and Metals, Less Reactive. Additionally, many organic compounds are weakly reducing but are categorized in other reactive groups based on their structures.

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.

Dibutyl phosphite, diethyl phosphite, ferrous chloride, ferrous oxalate, hydrogen, hydroxylamine sulfate, potassium oxalate, sodium tellurite, tris(2-chloroethyl)phosphite.