Which of the following is a disorder causing unpleasant odors from the armpit?

Bromhidrosis is the condition specifically associated with the production of unpleasant odors, particularly from the armpits. This occurs due to the breakdown of sweat by bacteria on the skin. The combination of sweat, particularly when excessive, and the presence of bacteria leads to the formation of odor.

Hyperhidrosis, while related to excessive sweating, does not inherently cause a foul smell; it is the amount of sweat combined with bacterial action that is significant in bromhidrosis. Dermatitis and psoriasis are skin conditions that can cause issues like inflammation and scaling, but they do not specifically relate to odor arising from the armpit area. Therefore, bromhidrosis is the most accurate choice when identifying a disorder causing unpleasant odors specifically from the armpit.