Chronic obstructive pulmonary disease (COPD) is a life-threatening condition. It affects your lungs and ability to breathe. The pathophysiology of the disease, or the physical changes associated with it, start with damage to your airways and the air sacs in your lungs. It progresses from a cough with mucus to difficulty breathing.

Unfortunately, the damage done by COPD can’t be undone. But there are some preventive measures you can take to lower your risk of developing COPD.

COPD is an umbrella term for several chronic lung diseases. The two main COPD conditions are chronic bronchitis and emphysema. These affect different parts of the lungs, but both lead to difficulty breathing.

To understand COPD’s pathophysiology, it’s important to understand the structure of the lungs. When you inhale, air moves down your trachea through two tubes called bronchi. The bronchi branch out into smaller tubes called bronchioles. At the ends of the bronchioles are little air sacs called alveoli. And at the end of alveoli are capillaries, which are tiny blood vessels.

Oxygen moves from the lungs to the bloodstream through these capillaries. Carbon dioxide moves from the blood into the capillaries and then into the lungs and exhaled.

Emphysema is a disease of the alveoli. The fibers that make up the walls of the alveoli become damaged. The damage makes them less elastic and unable to work when you exhale.

If the bronchioles become inflamed they produce mucus, which is bronchitis. If the bronchitis persists, you can develop chronic bronchitis. You also can have temporary bouts of acute bronchitis. But these episodes aren’t considered COPD.

The main cause of COPD is smoking. Breathing in smoke and chemicals can injure the airways and air sacs. This leaves you vulnerable to COPD. Exposure to secondhand smoke, chemicals, and even cooking oils in poorly ventilated buildings can also lead to lung diseases.

Serious symptoms of COPD usually don’t appear until the disease is advanced. Because COPD affects your lungs, you may find yourself short of breath after minor physical exertion. If you find yourself breathing harder than usual after a common activity, like climbing stairs, you should see a doctor. Tests of your respiratory health can reveal conditions such as bronchitis and emphysema.

One of the reasons breathing becomes more challenging is because the lungs produce more mucus and the bronchioles become inflamed and narrower as a result. With more mucus in your airways, less oxygen is being inhaled. This means less oxygen reaches the capillaries in your lungs. Less carbon dioxide is also being exhaled.

Coughing to help release the mucus from the lungs is a common sign of COPD. If you notice that you’re coughing more and producing more mucus, you should see a doctor. You can’t assume that your nagging cough is harmless.

As COPD progresses, many other health complications can follow. Besides coughing, you may notice yourself wheezing when you breathe. The buildup of mucus and the narrowing of the bronchioles and alveoli may also cause chest tightness. These aren’t normal symptoms of aging. If you experience them, see your doctor.

Less oxygen circulating throughout your body can leave you feeling fatigued. Lack of energy can be a symptom of many conditions. And it’s an important detail to share with your doctor. It may help determine the seriousness of your condition. In people with serious COPD, weight loss also can occur as your body requires more and more energy to breathe.

Read more: Early COPD symptoms »

One of the easiest ways to prevent COPD is to never start smoking or stop as soon as you can. Even if you’ve smoked for many years, you can start to preserve your lung health the minute you stop smoking. The longer you go without smoking, the greater your odds of avoiding COPD. This is true no matter what age you are when you quit.

It’s also important to have regular checkups and follow the advice of your doctor. There are no guarantees when it comes to COPD. But you can take steps to maintain better lung function if you’re proactive about your health.