[Alchemy] was one of many crafting skills that existed in Deep Karma. Basically, it acted as a specialization of the [Cooking] skill that allows for the production of status-altering substances, using ingredients collected from nature. These concoctions can range from potions, to poisons; aphrodisiacs to magical brews, depending on the ability of the alchemist.
Sonny was a Master level Alchemist, which was the highest tier possible for any skill.
Through years of experimentation, he'd discovered mixes for combating just about any malady, pest problem, or hex that ever threatened him and his brothers.
Indeed, the insect repelling perfume that his brothers would wear was of his own design.
The brothers' hut itself was protected against infiltration by all types of small animals, and by extension any Rakshasa disguised as such, as a result of his constant slaving over the fires of the cauldron.