1. Seasonal Allergies

Do spring allergies always have your nose running and your eyes watering? New studies have suggested that seasonal allergies can lead to depression. Allergies have serious physical effects, such as sleepless nights, fatigue, congestion, or headaches, and the physical toll makes a person more vulnerable to depression than people without allergies.

2. Smoking

Your habit of smoking may cause depression. It's often difficult to determine whether smoking comes first or depression because some people start smoking when they are depressed, while others smoke a lot and get depressed. Whatever the case, you should quit smoking because nicotine affects neurotransmitter activity and alters the levels of serotonin and dopamine that may have something to do with depression.

3. Thyroid Disease

The thyroid gland in the neck produces thyroid hormone that acts as a neurotransmitter and controls serotonin levels. A thyroid disease such as hypothyroidism may affect the production of thyroid hormone, which in turn will trigger the onset of depression and other symptoms, such as constipation, cold sensitivity, and fatigue.

4. Summer Depression

Seasonal affective disorder (SAD) has its connections with winter blues, and it causes problems for about 5% of Americans. This form of depression also hits many people in the summer because the body finds it difficult to adjust to new seasons with different temperatures. This may cause imbalances in brain chemistry and affect neurotransmitter activity, which may lead to depression.

5. Poor Sleep Habits

Sleep deprivation most often leads to irritability, but it may be an underlying cause of depression. The research has shown that sleep deprivation affects your brain activity, robbing you of time your brain cells need to replenish. This impairs brain function and can lead to depression.

6. You Don’t Eat Fish

Among many other surprising causes of depression is lack of fish in the diet. It is connected to the fact that fish will have loads of omega-3 fatty acids that the body needs to regulate neurotransmitters like serotonin. Not eating enough fish is more likely to cause depression in women than in men.

7. Your Location

Many studies have confirmed that people living in urban areas are at a greater risk of developing depression; in fact, you have a 39% higher risk of mood disorder if you're an urban dweller as compared to those in rural regions. It is due to this particular reason that depression rates are not the same in countries and states. Even altitude may affect your brain activity, which is the reason why suicide risk increases with altitude.

8. Facebook Love

While a romantic relationship and breakup over Facebook will most definitely lead to depression, you may find yourself in trouble simply because you're spending too much time in front of your PC. A number of studies have confirmed that excessive interaction over social-networking sites may lead to depression in preteens and teens. Facebook overload may make it difficult for you to maintain real-life human interaction. You may even have an unrealistic view of how things work in the world, which in turn will lead to "Facebook depression".

9. Birth Control Pills

Oral contraceptives can have side effects: they contain a type of progesterone that can cause depression in some women. The real reason why these pills lead to depression is still unknown, as not every woman who's on contraceptives faces the problem.

Have you been surprised by any of these things that can trigger depression?