H meaning in Medical ?

Mustard gas or sulfur mustard is a chemical compound belonging to the sulfur-based family of cytotoxic and blister agent chemical warfare agents known as sulfur-mustards or mustard agents. The name mustard gas is widely used, but it is technically incorrect: the substance does not actually vaporize into a gas, but instead disperses as a fine mist of liquid droplets.

Mustard gas has a long history of being used as a blister-agent in warfare and, along with organoarsenic compounds such as Lewisite, is the most well-studied of such lethal agents. Mustard gas can form large blisters on exposed skin and in the lungs, often resulting in prolonged illness ending in death. Pure sulfur mustards are colorless, viscous liquids at room temperature. When used in impure forms, such as warfare agents, they are usually yellow-brown and have an odor resembling mustard plants, garlic, or horseradish, hence the name.

As a chemical weapon, mustard gas was first used in World War I, and has been used in several armed conflicts since then, including the Iran–Iraq War resulted in more than 100,000 chemical casualties. Mustard agents are regulated under the 1993 Chemical Weapons Convention. Three classes of chemicals are monitored under this Convention, with sulfur and nitrogen mustard grouped in Schedule 1, as substances with no use other than in chemical warfare (though since then, mustard gas has been found to be useful in cancer chemotherapy). Mustard agents could be deployed by means of artillery shells, aerial bombs, rockets, or by spraying from warplanes or other aircraft.