Topical flame retardant is where a chemical treatment is applied to a fabric. When that treatment is exposed to flame a gas is emitted and oxygen precluded, causing the flame to be extinguished. As this is a topical treatment it can be subject to deterioration over time, and also the emitted gas is usually fairly toxic. Inherent flame retardant is where the fiber itself contains the flame inhibitor. The latter is a more permanent for the life of the fabric and cannot wash or wear off.