Everyone finds themselves in a bad mood once in a while. Usually it's clear to see what's causing you to feel badly - maybe you're coming down with a cold or there's something frustrating happening at work. Sometimes, however, it seems as if you're in the dumps for no reason at all. There are often subtle culprits in these situations - here are four things that can make your mood turn sour:

1. Comparisons

One of the worst things you can do for your mood is compare yourself to other people. The prospect is all too tempting, particularly when you factor social media into the mix. It's easy to see what's going on in your peers' lives and decide you're not stacking up. It's important to resist this urge, however. When you start to feel this way, make an effort to keep things in perspective. Remember that people tend not to broadcast their struggles and failings - you're only seeing their best sides. The odds are good that everyone you think is doing better than you thinks the same of you.

2. Your diet

If you're not eating a balanced diet, you might be suffering from mild-to-severe nutritional deficiencies. Eating the wrong foods (and skipping the right ones) puts your body under a lot of stress. If you're not sure why you're sad or upset, take a look at what you've had for meals lately. If it's a lot of junk food, you might have found your answer. Swap out chips and candy for fruits and vegetables, and use healthier cooking methods like grilling rather than frying your food. There's a decent chance your mood will improve once you're eating better.

Sometimes salad is the answer. Sometimes salad is the answer.

3. Multitasking

Very few people can multitask well. Even those who think they are excellent at doing multiple things at once are often actually terrible at it. What happens when you try to multitask and you're not one of the select few who have that talent? You get incredibly frustrated. Instead of trying to spread yourself over multiple projects at a time, focus all of your attention and energy on one thing. Even though this may feel less productive, you'll probably get more done since you won't have to go back and correct errors made the first time. Can't give up multitasking? The University of Newcastle has a test you can take to see if you can do it effectively. Be warned - it's hard.

4. Other people's moods

Even if you think you're not particularly susceptible to other people's moods, emotions tend to be pretty contagious. If someone is angry or irritable, he or she is more likely be short with or snap at you. It's easy to see how this can bring your mood down, as well. Take a good look at your friend group and see if there's anyone who is consistently negative. Try to limit your time around the people who regularly complain or gripe about their circumstances. Even though it's fine to vent once in a while, frequent grumbling - even about things with which you're not involved - can make your life seem worse.