Most acoustic guitars are constructed almost entirely from wood. While that means they can be somewhat durable based on the quality of their construction and finish. Naturally, they can be subjected to damage by factors that create an ‘unhealthy’ environment (unhealthy for the guitar itself, that is…).

One of the most common forces of nature (along with extreme temperatures) that can affect both the playability and the guitars overall construction is humidity. If an instrument such as an acoustic guitar is left subject to the wrong humidity levels, things can get nasty.

In this multi-part series, we will talk ‘all about humidity.’

What is humidity? What the right specifications for good guitar health are. What can happen if the humidity levels aren’t correct?
Also, learn about several kinds of accessories that can keep your guitar in like-new condition.

What is humidity?

Humidity is simply a way of measuring how much water vapor there is in the air. It is often expressed in terms of ‘relative humidity.’ Relative humidity can be defined as the amount of water vapor in the air expressed as a percentage.

Think about going outside on a hot day when a rainstorm may be on the way. The air tends to feel thick and ‘wet.’ In those cases, the relative humidity is typically pretty high.

Here’s a more relevant example: the thing about the last time you went into your local guitar store (yes, I mean a real brick and mortar store, and yes – they still exist in this day and age of internet shopping). Some of them have special rooms dedicated to only acoustic guitars. Did you notice that the overall environment seemed to be a bit warm and muggy? That’s because the relative humidity was set to the right point to keep their inventory in tip-top shape.

Hey – you didn’t expect to get a science lesson today, right? No worries – no homework or tests to take today!

What is the right relative humidity level for an acoustic guitar?

You’ve probably noticed by now that we’ve been referring pretty much exclusively to acoustic guitars. That’s because acoustic guitars can obtain the most damage from being stored in an environment with an incorrect humidity level (sure, electric guitars can be affected as well, but we’ll go into more details on that later).

Guitar humidity hygrometer and humidifier

The best relative humidity level for an acoustic guitar (based on recommendations from many of the best manufacturers) is typically in the 45% to 55% range. Remember that wood, by its inherent nature, is a porous material – meaning that it is susceptible to humidity. Suppose an acoustic guitar is kept in the wrong environment for a prolonged period. In that case, the effects can range from minor inconveniences to significant damage beyond repair.

Effects of not enough humidity

Suppose an acoustic guitar is stored in an atmosphere with a relative humidity level that is too low. In that case, the most likely effect will be that the wood will shrink due to the lack of moisture. That can lead to issues such as poor playability along with – in extreme cases – severe cracking.

One of our staff writers has some first-hand experience with this – we’d recommend taking this as a vast ‘lessons learned’…

“I had just bought my first real acoustic guitar – one that was a level above many beginner-style instruments. While it wasn’t the most expensive guitar on the rack that day, it certainly wasn’t the cheapest – it was the most money I had ever invested in a guitar at the time.

While I did store it in a decent case, I really didn’t know the best way to care for it. Truthfully, I never even thought about it all that much – and that was a BIG mistake on my part.
Over time, I started to notice that the action just wasn’t as good as it was when I bought it.

I was beginning to get fret buzz a lot, even to the point that some notes were completely fretting out. I had just figured it needed a setup. I didn’t realize at the time that I was seeing warning signs of more significant problems, so I didn’t put a priority on getting it fixed right away.

About a week later, I opened the case and – to my absolute horror – there was a massive crack on the top (it was a solid spruce top, by the way) that ran all the way from the bottom of the bridge to the end of the guitar by the endpin for the strap. I called up the store I bought it from, and they told me I hadn’t kept it at the right humidity level – it had dried out to the point of failure.

So I got a guitar humidifier to fix the problem, but the damage had been done. Sometime later, the entire bridge lifted off the top. The moral of the story? If you invest in a top-notch acoustic guitar, educate yourself on how to properly care for it. If you don’t, the end result may be catastrophic.”

True story, sad to say…but it happens to more acoustic guitars than you may think.

Effects of too much humidity

Having an acoustic guitar live with too much relative humidity can be just as bad as not having enough. High relative humidity levels will make the wood too ‘wet.’ While it surely won’t crack, there are definitely adverse effects that can be just as damaging.

What you most likely experience in a guitar that is too wet is that the wood will swell up. That can lead to:

  • Unusually high string action
  • Poor tone due to the extra water that is being held in the wood
  • Failure of glued joints
  • Finish defects
  • Distortion of various parts of the guitar (such as the neck)

What’s worse is that some of the damage can be permanent – even if the guitar ends up being stored in the right relative humidity environment. Some conditions may correct themselves, but extreme wood distortion may be hard – if not impossible – to reverse once it occurs.

Conclusion

Wood is the perfect material for an instrument such as an acoustic guitar. Still, it is far from being ‘hands-off’ or ‘carefree.’ Any instrument needs to be correctly taken care of. Keeping an eye on the humidity levels is critical to keep your guitar playing, sounding, and looking as it did on the day you brought it home.

There is an acceptable range of relative humidity that will keep your guitar happy. To be sure, spending some limited time in a dry or wet environment isn’t always a cause for concern. We all have been in situations where the room is too dry or played an outside gig where the air is very muggy. The key is to keep it stored under the right conditions as much as possible.

In our next installment, we will discuss several guitar accessories that can keep your acoustic at the right relative humidity levels. Some are relatively inexpensive, and some may have more functionality, but they may cost a little more.

Until next time – keep your best acoustic out of the desert and also out of the rain!

Discuss your guitar’s humidity levels with others in our guitar community chat forum.