Perfumes and colognes are made from a combination of essential oils (often referred to as "base notes") and alcohol. The essential oils are usually extracted from flowers, herbs and other substances that contain strong, pleasing scents. Only a small amount of essential oil is needed, since the scent is usually in its most concentrated form.
Once the perfume or cologne touches your skin, the next part of the fragrance process starts. This is when your natural body heat makes the perfume or cologne to heat up and evaporate, causing the fragrance to emit from your body and become more noticeable.
Your Personal Chemistry
Along with your personal body heat, the chemicals your body emits can also affect how well a perfume or cologne works. As the fragrance from the essential oils interacts with your personal body chemistry, chemical reactions produce new fragrances. This is why a cologne may smell completely different then what you smelled from a tester or when someone else was wearing it.
A powerful way that a perfume or cologne works is through sensory memory. A cologne your father wore or a perfume your mother wore may later attract you to or repel you from someone who wears that scent. The same works for first loves and bad breakups. Even certain everyday smells such as pine, cedar, roses or laundry detergent may cause you to be attracted or repelled to similar scents, depending on your experiences with them in the past.