Your guitar is made of wood, and wood never stops reacting to the air around it. Of everything that affects how a guitar plays, sounds and lasts, humidity is the big one. Acoustic or electric, cheap or expensive, every guitar moves when the moisture in the air changes.
This guide explains what’s going on inside the wood, what too much or too little humidity does to your guitar, and the simple things you can do to protect it.
Why Wood Reacts to Humidity
Wood naturally takes on and gives off moisture to match its surroundings. This is called hygroscopicity. When the air is damp, the wood absorbs moisture and swells. When the air is dry, it releases moisture and shrinks.
Most guitars are happiest at a relative humidity of roughly 40 to 50%, close to the conditions they were built in. Stray far outside that range for long and you’ll start to see problems with playability, tone and eventually the structure of the guitar.
In the Netherlands you get both extremes. Summers are often damp, and once the central heating goes on in autumn, indoor air can become very dry. We wrote about that seasonal shift in Is Your Guitar Ready for Autumn?
What High Humidity Does to Your Guitar
Above roughly 60% humidity, the wood takes on extra moisture and starts to swell.
Swelling wood
You won’t see it happen overnight, but over time swelling can distort the body and neck.
- Acoustic guitars are the most sensitive. The top (soundboard) and back can bulge outwards, which raises the string action and makes the guitar harder to play.
- Electric guitars are more stable thanks to their solid bodies, but the neck can still swell, which affects stability and tuning.
Higher action and harder playing
As the wood swells, the neck usually gains relief (forward bow) and the strings sit higher above the frets. Higher action means pressing harder to fret notes, which makes fast or detailed playing more tiring. On acoustics, a swelling top can also lift the bridge and raise the action further.
A bowed neck
Long periods of high humidity can leave a neck noticeably bowed. That throws off intonation and needs a truss rod adjustment to correct. Left alone for too long, it can lead to more serious problems.
A duller tone
Wood that’s full of moisture doesn’t vibrate as freely, so the guitar can sound muffled and less lively. You’ll notice this most on acoustic guitars, where the wood does so much of the work.
What Low Humidity Does to Your Guitar
Below roughly 35% humidity, the wood dries out and shrinks. This is often more damaging than high humidity, and it’s the main risk during a Dutch winter with the heating on.
Cracks
The most serious problem. As the wood contracts, the stress can crack the top, back or sides. Acoustic guitars, with their thin solid-wood tops, are the most at risk. A crack can be a hairline or a proper split, and it affects the sound, the structure and the value of the guitar.
Sharp fret ends
The fretboard shrinks, but the metal frets don’t. The fret ends then stick out past the edge of the neck. These sharp fret ends (also called fret sprout) catch your hand when you move along the neck and need to be filed down. It’s a classic winter problem.
Low action and fret buzz
As the neck dries, it can lose its relief or even bow backwards. The strings drop closer to the frets and you get fret buzz, often in the lower positions, along with less sustain and a thinner tone.
Loose glue joints
Guitars are glued together at the neck joint, the bridge and (on acoustics) the internal braces. In very dry conditions glue joints can weaken, and parts like the bridge can start to lift. That’s a bigger repair, so it’s worth preventing.
How to Protect Your Guitar From Humidity
The good news is that most humidity problems are easy to prevent.
Use a humidifier or dehumidifier
- Soundhole humidifiers sit in the soundhole of an acoustic guitar and slowly release moisture. Very useful in winter.
- Case humidifiers and two-way humidity packs keep the air inside the case at a steady level, protecting the body and the neck.
- Room humidifiers or dehumidifiers control the whole room. Ideal if you keep several guitars on stands or wall hangers.
Measure the humidity
A small digital hygrometer costs a few euros and tells you exactly what’s going on in the room or the case, so you’re not guessing. Aim for 40 to 50%.
Keep it in its case
When you’re not playing, a good case gives your guitar a stable little environment of its own. This makes the biggest difference when the weather is extreme.
Avoid sudden changes
Keep your guitar away from radiators, heaters and direct sunlight, and never leave it in a car. When you move a guitar between very different conditions, such as from a cold car into a warm house, leave it in the case for 20 to 30 minutes so it can adjust gradually.
Condition the fretboard
Unfinished fretboards like rosewood and ebony benefit from regular conditioning, especially before the dry months. We use our own GuitarBuddy Fretboard Wax & Conditioner, and you can read why we prefer it to lemon oil in this article.
How Often Should You Check?
- Every week: glance at your hygrometer.
- Every month: check your guitar for sharp fret ends, changes in action or any signs of cracks.
- Every season: take extra care as the weather changes, and adjust your humidifier or dehumidifier.
A seasonal setup is the easiest way to keep on top of all this. Read why regular guitar setups matter for more on what a setup involves.
Conclusion
Humidity affects every guitar, but with a hygrometer, a bit of attention and a stable place to keep your instrument, you can avoid almost all of the damage it causes. Keep your guitar at a steady 40 to 50% and it will play better, sound better and last longer.
Worried About Your Guitar?
If your guitar has started buzzing, the action has changed or the fret ends feel sharp, it probably needs a setup to suit the season. GuitarBuddy is based in Zandvoort and works with players in Haarlem, Aerdenhout and Amsterdam. Have a look at our guitar setup and repair services or book your guitar setup.
