If I may add to this question, were chemical weapons produced by any nation in the war?

I would direct your attention to the numerous similar questions that have already been asked on this sub. There is in fact a small FAQ section devoted to such questions. Always a good idea to check the FAQs first.

In short, gas is, in most situations, not really a very effective weapon. It's not like a nuke that will allow you to win the war; it just causes a lot of unnecessary suffering.

Also, if the Germans or the Japanese used gas on the Allies, then the Allies would be justified in using gas as well. But gas is better as an offensive weapon than as a defensive weapon, so it would not be logical for the side on the defensive (as the Axis were) to initiate the use of gas.

The Japanese were particularly concerned with this, since they tended to hide out in caves, which are actually one of the best situations for an attacker to use gas. Therefore, they took all measures to avoid having the Allies use it:

Fear of Japanese retaliation [to chemical weapon use] lessened because by the end of the war Japan's ability to deliver gas by air or long-range guns had all but disappeared. In 1944 Ultra revealed that the Japanese doubted their ability to retaliate against United States use of gas. 'Every precaution must be taken not to give the enemy cause for a pretext to use gas,' the commanders were warned. So fearful were the Japanese leaders that they planned to ignore isolated tactical use of gas in the home islands by the US forces because they feared escalation.