Don’t think of it as “making a change” in a woman’s brain. Think of it more as simply the way a woman’s brain already works. There have been some crazy hits reported, and I have seen a few blatant ones myself (a couple of them with AMMO), even in my very limited experience, but effects I think tend to be more on the subtle side for most people.
Because pheromones work on a subconscious level, the effects are usually displayed subconsciously. Don’t expect real-life versions of Axe commercials, and you won’t be disappointed.
For your question: “How do they work?”
Well, simply put, the theory goes: synthesized pheromones mimic the chemicals that people naturally excrete in the forms of urine, sweat, saliva (?), copulins, etc. They are natural biological indicators of status, potency, strength, and fertility. The pheromone “sixth sense” seems to be closely related (but not identical) to the sense of smell. Humans are naturally “preprogrammed” to have certain reactions to these chemicals, just as they have reactions to another person’s muscle tone, posture, height, and figure.
Why it works is a topic of some debate and depends on whether you believe in evolution or intelligent design. An evolution proponent will say that we inherited these senses from our animal ancestry. Pheromone reactions are extensively documented in the animal world. A creationist/IDer (such as myself, though I realize there are probably not a whole lot of us here) will say that the same God who designed animals to have certain senses of sight, smell, taste, touch, etc. also designed humans with these senses. And one sense we have in common is pheromones. Either way, it works.
The reason synthetic enhancements are particularly effective is because of our modern hygenic habits. We bathe quite frequently compared to people thousands of years ago, and so we wash off most of our natural phero output along with the grime and the sweat. Synthetics can help make up for that loss, as well as help us to fine-tune the signals we send out. Since everyone else is washing off their phero-signatures and not replacing them with anything other than diluted essential oils (cologne), you can stand out from the crowd.