It's not likely that you need to switch deodorants because your body has simply gotten used to your deodorant, but there are several different reasons why your deodorant might not be working as well anymore.
During our lives, we experience hormonal changes that can also impact how much we sweat and how much bacteria that gets produced. If you experience big changes in your body's hormones, such as getting pregnant, breastfeeding, going through menopause or just aging, your sweat output and odor might also change. Some medications and medical conditions also cause you to sweat more.
Dietary choices can also affect your sweat production or your body odor. These include increasing or decreasing your intake of foods like garlic, curry, cumin, caffeine and sugar. Similarly, if you go from being a couch potato to hitting the gym every day, you're going to get sweatier. Big life changes can bring about increased stress levels, which also can mean an increase in sweat output.
We typically sweat more in hotter times of the year or in hotter climates, so a single deodorant might not work for you year-round. For example, you might be able to use just a deodorant in the winter but need a deodorant/antiperspirant in the summer. You might also need a stronger product when you're working out, but use a different one when you're just going back and forth to work.
There are some things you can do to improve your deodorant's staying power. Some antiperspirants are designed to be applied at night, which gives them more time to be absorbed into the pores. These typically contain aluminum chloride, which is often found in prescription strength deodorants. Making sure to apply deodorants to clean, dry armpits will also help, and so will shaving or trimming armpit hair, which can hold in bacteria.
If you've tried a lot of different deodorants and nothing seems to work, or you sweat excessively in places other than your armpits, consider visiting a doctor. Hyperhidrosis, or excessive sweating, affects about 3 percent of the world's population and there are many treatment options available [source: International Hyperhidrosis Society].
For lots more information on sweating, deodorant and related topics, check out the next page.