First, Never store your fragrances in the sunlight. The biggest concern is the break-down of the delicate top notes such as the citrus based notes in a fragrance. Heat and sunlight are the enemy. Storing them in the bathroom may seem like the logical place, but the heat, humidity, and bright lights will damage the top-notes over time. I store mine in the bedroom, in a location that gets only diffuse light. You may hear people say that they store their bottles in the refrigerator. This is unnecessary. Without getting too scientific, as a liquid heats up, molecules bump into each other faster, and this causes some of the oils to evaporate out of the perfume. As long as you keep them below about 85 degrees Fahrenheit you are fine. This is the same reason some people say you shouldn't rub your wrists together when you apply the fragrance, you could be generating heat that will break down your top notes quicker. A slight rub to spread it around is fine, but don't press so hard that you feel it warming up. You can't "damage the molecules"... they are far too small to damage by rubbing!!!!
You may hear people say cologne "expires" This also isn't necessarily true either. I know people who have vintage 1950's bottles that are still good. If stored in a cool dark location, they will last for years. Last summer I put about 10 strips sprized with different fragrances in the hot car for several days. It got up to well over 100 degrees. They still smelled fine after a day, but after a week, they had all degraded to a common smell of ...Powder. Strange. So, don't keep your bottles in a hot car.