Why mutual deterrence restrained chemical warfare in World War II

Why were chemical weapons not used in combat between the major European powers during World War II?

Both sides feared retaliation and overestimated the other's stocks, so initiating chemical warfare looked too dangerous.

Reciprocal deterrence discouraged the major European powers from starting chemical warfare during World War II. Both sides possessed chemical agents and feared retaliation. Each also overestimated the other's stocks, so the expected response appeared larger than the real inventory. Britain deliberately encouraged German overestimation, while British planners distrusted German claims about their capacity. Uncertain intelligence raised the perceived cost of escalation.