Your immune system is a part of your body’s natural workload. Just like good circulation, a healthy digestive system and a strong heart and lungs, immunity can thrive or fail depending on your health.

So a healthy lifestyle can help you fight infections and be more resilient – but many bad habits, like these ten, are natural-born killers for your body’s first line of defense.

1. Lack of sleep

Sleep is your body’s one respite for the trials you put it through when you’re awake. It uses the down time to regenerate in a variety of ways, from healing to strengthening, and your immune system is no exception to those benefits. Without the proper rest, your immunity will never have a chance to recharge from what weakens it when it’s awake and busy fighting things like infection.

2. Stress

The hormone cortisol, released in stressful situations, suppresses things that would be non-essential in fight or flight situations, including immune responses and other functions. The calmer, happier and more stable you are, the more your immune system will thrive.

3. Not drinking enough water

Hydrating properly – that means with good old H2O, not energy drinks or sugary juice – helps flush toxins from your system, which means one less thing for your immune system to worry about.

4. Drugs and alcohol, smoking

Alcohol can be detrimental to your white blood cell count, a vital asset to good immunity, and it deprives your immune system of nutrients it needs. Drugs like marijuana also prevent nutrients from finding their way into your system.

And like the rest of them – but perhaps most chronically of all – smoking is the fastest way to bring harmful toxins into your system, which means your immune system is going to expend valuable energy and resources trying to get rid of them, and perhaps divert its attention from things it should be fighting instead.

5. Fatty, sugary foods

Your immune system is part of the bodily functions that are supported by good nutrition and general good health. This means that the worse your diet, the worse for your immunity. Red meat, refined carbohydrates like white flour and sugar and high-fat dairy are all rich in saturated fat, which increases cholesterol and puts you at risk for problems like diabetes and heart disease.

Meanwhile, things with a lot of trans fat, like margarine or butter, contribute to low-grade inflammation, which occupies your immune system when it should be busy fighting more important things. But plant-based oils are a good substitute – and the most immunity-oriented diet contains a lot of fruit, vegetables, whole grains and fatty fish.

6. Frequent weight changes from sporadic dieting

Dramatic weight fluctuations have been shown to drastically decrease the ability of your immune system to fight off infections and even things like cancer. A consistent weight over time, meanwhile, promotes a healthy immune system.

7. Lack of exercise

Just like everything that promotes good health, good exercise strengthens your body and makes it function at a higher level, including in the immunity department.

8. Too much exercise

Overexerting is stressful for your body, which requires a delicate balance in all things. If you work too hard or run yourself into the ground, you’re lowering your defenses, tiring out your body, and putting yourself at risk for infection.

9. Sun overexposure or tanning

High levels of UV rays spell trouble for your immune system, and tanning is even worse – specifically, three times worse. Tanning beds blast your body with three times as much UV rays as you get in normal sunlight, which weakens the resiliency of your skin cells, your body’s first defense against many problems. And the more you chip away at your resiliency, the less your body will be able to fight off more serious infections down the line.

10. Antibiotics

Think there’s no way something meant to make you healthy could do just the opposite? Think again, because what doesn’t kill bacteria makes them stronger. The bacteria left over when antibiotics have killed off most of the infection, survive because they were able to mutate against the antibiotic.

Antibiotics also kill “good” bacteria, like those in your intestines, as well as the “bad,” which cause infections.