[intro ].

If you’ve ever smoked cigarettes, you’ve probably been told at some point to stop smoking after an injury or medical procedure. With the many very good reasons smoking is unhealthy in general, you might think doctors are just taking whatever opportunities they can to tell you to quit.

But the reason they give you those instructions is about more than just lung cancer. Smoking actually makes wounds take longer to heal. We’ve known about this problem since the late 1970s, and since then, researchers have discovered a bunch of different mechanisms behind it.

For context, there are four main phases of wound healing. First, your body stops the bleeding by forming a clot. Next, your inflammatory response kicks in, defending against infection and preparing the wound for repair.

Then, your body starts to fill in the area with new tissue, shrink the wound, and cover it up with new skin. Finally, the area gets stronger and more flexible. Smoking interferes with every single one of these stages.

Strangely enough, smoking can actually make it easier for clots to form, which sounds like good thing. But the chemical composition of the clot is different which makes it take longer for your immune system to start preparing the wound for healing in the second phase. So, it’s not worth the trade-off.

In phases 2-4, the main issue is that cigarettes lower the amount of oxygen moving through your body. The nicotine, carbon monoxide, and hydrogen cyanide you absorb when you smoke have all been shown to lower the concentration of oxygen in your tissues. And oxygen is a critical part of wound healing.

Your immune system needs it to defend against infection properly and to get your immune cells where they need to go. It’s also important for making collagen a protein used to make the tissue that fills in the wound and strengthens the area in stages three and four. The problems in those two repair-focused phases go beyond just oxygen, though.

For example, nicotine also causes your body to produce enzymes that can make the tissue damage worse. So you can see why doctors would recommend that you stop smoking after an injury or surgery. When it comes to healing, it’s just a bad situation all around.

Unfortunately, even if you immediately stop smoking when they tell you to your body still won’t heal the same way a non-smoker’s would. Don’t get me wrong — it helps, especially with the immune response that’s so important for protecting against infection and getting the area ready for repair. But studies have found that the third and fourth phases where the tissue fills in and strengthens, can take months to go back to normal.

So if you do get injured or have surgery and your doctor tells you to stop smoking afterward, you should definitely listen. But if you want to get the full benefits — not to mention reduce your risk of all kinds of other health issues — it’s better to stop as soon as you can. Thanks for watching this episode of SciShow, and thanks to all our patrons on Patreon who made it possible!

We’re grateful to have you. If you want to submit a science question and help us make more videos like this, you can go to patreon.com/scishow. [ outro ].