Is Lactic Acid Bad? What It Is and What It Actually Does in Your Body

Let’s clear something up first

That burning feeling you get mid-workout, the one that makes your legs feel like they’re on fire? That’s not just lactic acid. In fact, it’s not even technically "acid" at all.

So is lactic acid bad? It’s time to unpack what lactic acid actually is, why your body makes it, and why it’s not the enemy it’s been made out to be.

What is lactic acid?

Lactic acid (more accurately, lactate) is a naturally occurring substance in your body. It’s a key part of how we produce energy during movement, especially when intensity climbs.

When you're exercising, your body creates energy in two main ways: aerobically (with oxygen) and anaerobically (without oxygen). Which one it uses depends on how hard you’re working.

When does lactic acid build up?

During high-intensity efforts, your body often taps into anaerobic metabolism first. It produces energy quickly without relying on oxygen. That’s when lactic acid starts to build. It’s your body’s way of keeping the engine running when things heat up fast. It can make your muscles burn, leave you feeling wobbly, and push your system into temporary overload. But it’s not a bad thing.

On the other hand, during lower-intensity efforts like walking, light jogging, or steady cycling, your body uses aerobic metabolism. In these situations, lactic acid doesn’t accumulate the same way because your body has time to keep up with the demand.

Does lactic acid cause muscle soreness?

No. And this is a common myth.

That deep, aching soreness you feel a day or two after a tough workout is called DOMS (Delayed Onset Muscle Soreness), and it’s caused by tiny tears in your muscle fibres and the resulting inflammation, not by lactic acid.

In fact, lactate levels typically return to baseline within an hour after exercise. So if you're sore the next day, lactic acid isn’t the one to blame.

So… is lactic acid bad?

Not at all. Lactic acid isn’t just a byproduct it’s actually a valuable fuel source. Your body can recycle it into energy, thanks in part to your liver, which helps convert it back into usable fuel through a process called the Cori cycle.

It also plays a role in increasing blood flow, sustaining high-intensity efforts, and improving overall performance. In fact, many athletes train specifically to raise their lactate threshold the point where lactate builds up faster than the body can clear it to enhance endurance and efficiency.

The takeaway

Lactic acid has been misunderstood for years. It’s not the villain behind soreness or fatigue. It’s part of how your body adapts, performs, and recovers.

Next time you feel the burn, know that your body’s doing exactly what it’s designed to do. Lactic acid is helping you stay in the game.

👉 Want to go deeper? Book a session with our team to learn how your body responds to different types of training, and how to use that knowledge to move better, recover smarter, and perform stronger.