Those tiny drops of perspiration that make up part of our bodies cooling system . We sweat when we do hard physical work . We sweat when we exercise . In these situations we can say we “work up a sweat .” For example , running is a great way to work up a sweat . We also sweat when it is hot outside . But we wouldn't say we worked up a sweat . We didn't do any work . We just got sweaty by being hot . We often use another verb when talking about sweating : break . For example , when I helped my friend move to her new apartment , I barely broke a sweat . That is because she doesn't own very much . I just needed to help her move some books , kitchen items , a box of clothes , and a cat . Now , there are other situations when people may sweat . When we are very scared , nervous , worried , or simply uncertain about something , we could sweat . If any of these feelings go to an extreme , we might say we “broke out in a cold sweat .” Sweating can also be a sign that you are unsure of your ability . That is why one popular advertisement for underarm deodorant had this famous expression : "Never let them see you sweat ." Sweating could also be seen as a sign that you lying -- or at least not telling the whole truth . If you watch crime shows , sweating is one thing police look for when they question a suspect of a crime . Now , sometimes we use the word sweat in a strange way . Let's say you help someone do something . But it was really not a big deal for you . The person thanks you . And you can say to them , “No sweat !” This just means it was easy for you to do . But I would only use this with someone I know fairly well . Here is another strange expression : "Don't sweat it ." This is a way of saying “no problem ” or “don't worry about it .” Here's a quick story . One time , my roommate and I decided to have a stoop sale . This is a fun way to get rid of stuff and make a little money . In the morning , we worked up a sweat carrying all the items down . But once things were set up , we could relax and talk to people who stopped by . It was really fun to get rid of things we no longer wanted . And by the end of the day we had earned nearly $100 to spend on a little party for everyone . It was a really hot day and during the sale , I sweated up a storm . So , I took off my favorite jacket and set it aside . By the end of the morning , I couldn't find it . My roommate asked me , “Was it the black jacket with lightning on it ?” “Yes ," I answered . She quietly said , “I think I sold it .” I could tell that she felt badly . So , to make her feel better I said , “Don't sweat it ! It's not a big deal . Come on , let's order pizza and drinks !” Inside , though , I must admit … I was a little upset . It was my favorite jacket . But those feelings did not last long . There are too many serious problems in life . So , it is important to not get upset about small things . In other words , don't sweat the small stuff . Here is my last note is on usage . While “sweat ” and “perspiration ” are physically the same thing , the two words are often not used the same way . We do not say “perspiration ” in the same informal way we say “sweat .” So , with all of the expressions we heard today , we only use the word “sweat .” We would not say we “worked up perspiration ” or “broke perspiration .” And we definitely would not say , Don't perspire the small stuff . But if you make a mistake ... don't sweat it !