The truth about dull knives is they are inevitable – and dangerous. A dull knife can slip and slide over your ingredients and require applying more pressure to make a full cut, resulting in higher chances of losing control of the knife and cutting into something other than food (like your fingers). Nicks and cuts from dull knives also take a lot longer to heal compared to the clean cut of a sharp blade.

No knife stays sharp forever, and they don’t sharpen themselves, either. However, most people go about creating everyday meals without realizing their knives aren’t cutting as well as they did right out of the box. Knife blades deteriorate gradually through regular use, so there’s simply no avoiding the dulling of a knife. However, there are other contributing factors that can and should be avoided to help prolong that sharp edge.

So, how can you tell if your knives are dull and what can you do to prolong their sharp edges? There are actually a few different ways to test the sharpness of your knife.

Here’s what we’ll cover in this guide:

We’ll also cover other reasons your kitchen knives go dull and what you can do to keep them in tip-top shape!

Top Signs of Dull Kitchen Knives

How do you know if your knives are dull? If you’re like me, you probably never noticed and have continued watching your vegetables fly across the kitchen like the “slippery little sucker” in Pretty Woman. Apparently, that’s not supposed to happen. And a mashed tomato is not the same as a sliced tomato.

So, how do you tell the difference between a sharp knife and a dull knife? Do you throw them at a wall and see which one sticks? Probably not, but that could be fun. Do you slide your finger across the edge of the blade to see how easily it slices through your skin? Well, you can but there are other ways that don’t involve treating your fingers like they haven’t done anything for you lately. Instead, check out these obvious signs and other ways to test the sharpness of your knives.

The Mushy Tomato

Much like a man who denies he’s in love, the tomato is tough on the outside and mushy on the inside. It takes a special someone (sharp knife) to to pierce through the skin and get to the mushy inside without making a mess. So, if you’ve ever sliced through a tomato and ended up with a mushy mess, then chances are you’ve met a dull knife (and ate a very messy BLT).  

It really doesn’t have to be this way though – you can perfectly slice a tomato and build a photo worthy BLT (because what would social media be without everyone posting photos of their meals?). All you need is a sharp knife (and bacon and lettuce and tomato and bread and maybe mayonnaise, if that’s your fancy).

So, what type of knife is best for this tomato test? Well, there are debates about the best knife to use for slicing a tomato – straight edge vs. serrated, chef’s knife vs. Santoku, and there’s even a “tomato knife” – but none of that matters because it’s really about preference and the sharpness of your knife. Any sharp knife should be able to easily break the tough skin of a tomato and create evenly cut slices with juices still intact.

Check out the video below to see how easily a sharp knife cuts through a tomato:

The Slippery Onion

Now, the onion is one slick vegetable, and not because it’s sneaky (you definitely know when an onion has been around). It’s because of its slick skin. If you’ve tried to cut through an onion and noticed your knife slips and slides all over the skin like that one last piece of rice on your plate that slides around your fork, then you’ve met a dull knife (and a slippery onion). 

Using a sharp knife to cut onions is also an expert tip for keeping those tears at bay! Check out our guide on how to cut onions without crying to learn all about why onions make you cry, which ones make you cry the most and what tricks actually work

Also check out the video below to see how easily a sharp knife cuts through an onion:

The Cracked Pepper

No, not the kind of cracked pepper that the one guy whose only job at the Italian restaurant is to come to your table and ask, “Cracked pepper?” while holding up the fancy pepper grinder. We’re talking about bell peppers that make a loud cracking sound during the chopping process. 

That cracking sound actually comes from rigid cuts (from a dull knife). So, unless you’re really into sound effects (and enjoy watching pieces of bell peppers propel across your kitchen), you’ll definitely want a sharp knife when it comes to chopping bell peppers.

Check out the video below to see how easily a sharp knife cuts through bell peppers:

Try the Tomato, Onion and Pepper Test With This Recipe: Pina Colada Guacamole

The Splitting Carrot

Do you remember that thing you used to do when you were a kid where you’d stretch your legs out with one in front and one in back then lower your body to the ground? Yeah, I couldn’t do that either, but apparently it’s called a “split” and as it turns out, carrots can split…add that to “being healthy” and that’s at least two things a vegetable can do that I can’t.

Anyway, it doesn’t take rocket science to properly slice a carrot, but it does take a sharp knife, as in you should easily slice right through a carrot without any force. So, if you’re slicing through a carrot and notice it begins to do that split thing when the knife is only halfway through, then you definitely have a dull knife.

Another way to test a knife’s sharpness with a carrot is to hold the carrot out in front of you with your non-dominant hand. Then, pick up the knife with your dominant hand and chop off the top of the carrot in one swift motion (like a ninja). Just be sure you are slicing away from yourself when you try this (unless you really are a ninja and know how to dodge a knife attack against yourself).

Check out the video below to see how easily a sharp knife cuts through a carrot:

Level Up Your Knife Skills: The F.N. Sharp Guide to Knife Cuts

The Paper Test

The paper test is super fun for testing the sharpness of your knife. Simply find that bill you hate to pay (or weren’t planning on paying anyway) and hold it out in front of you at shoulder height. Now pick up the knife with your dominant hand and press the blade down on the edge of the paper, slicing away from yourself (unless you’re a ninja).

A sharp blade should cleanly slice right through the paper with ease. A dull knife will either tear the paper unevenly or skip along the edge (this could also be a sign that you should probably pay that bill).

The Close Shave

We definitely recommend trying one of the above tests before attempting this one, but if you’re really that bold and curious, you can really tell a knife is sharp if it easily shaves off some arm hair. Just make sure you gently slide the blade across your arm at an angel to avoid cutting through the skin. If you have to press down too hard, then you’re definitely working with a dull knife.

5 Reasons Your Kitchen Knives Might Be Dull

Now that you know how to tell if your kitchen knives are dull, let’s take a look at the most common (and avoidable) reasons why it happens – aside from daily use, of course.

1. You Don’t Store Them Properly

Not using proper knife storage can also lead to a dull blade – and if you throw your knives in a drawer with the rest of your silverware and utensils, then you’re definitely guilty of not following the rules for caring for your kitchen knives.

While those knives are sliding around in that drawer, their delicate sharp edges are taking a hit, resulting in a dull edge – and potential nicks and scratches! Not to mention, storing sharp knives this way also isn’t a great way to treat your fingers as you can easily catch the edge of the blade while reaching in the drawer for other things.

Save your sharp edges (and your fingers) by investing in the best knife storage for your kitchen, like this magnetic knife block from F.N. Sharp 😜

Get All of the F.N. Sharp Essentials: The 6-Knife Set & Magnetic Knife Block

2. You Put Them in the Dishwasher

Dishwashers are great for cleaning food off of plates and silverware, but they can do lasting damage to kitchen knives. If you put your kitchen knives in the dishwasher, they can bang against other utensils and leave you with a scratched, chipped or dull blade. While there are ways to prevent this from happening, it’s the harsh environment of the dishwasher that you really need to worry about.

Heat treatment is essential to the knife making process as it’s used to alter both the chemical and physical properties of the steel, which falls under the realm of metallurgy. Heat treatment can involve several steps, but the ultimate goal is to bring the steel to a hardened state so it can hold a sharp edge. Although the dishwasher may not get hot enough to melt your blades, the heat combined with the detergent can alter the properties of the steel and lead to corrosion

There is a difference between soap and detergent. One of the reasons why dishwashers do their job so well is because they use harsher detergents, which act as surfactants. All dishwasher detergents are corrosive to some degree. That’s how they break down grime and grease. There isn’t much to fear when it comes to regular silverware but corroding a delicate knife’s blade will dull the edge considerably.

The best way to wash a knife is by hand with a soft cloth and warm, soapy water, making sure to keep the blade pointed away from your body. Instead of air drying the knife (which may cause rusting) you should wipe the knife gently dry with a towel in slow, vertical motions – not horizontally along the knife’s edge – then properly store the knife in a knife block, on a magnetic strip, or in a drawer with the blades covered and protected.

3. Your Cutting Board is Too Hard

If you’re cutting on a glass, marble, or granite counter or cutting board, you are damaging your knife’s edge with every cut. This is also true of many composite and even plastic cutting boards. The harder a cutting surface is, the more it impacts the knife’s cutting edge every time they come in contact.

Despite many modern advances in material sciences, old-fashioned wood is still the most knife-friendly cutting board material you can find. The softer the wood is, the better your knife will respond, like with this beautiful Acacia wood cutting board from F.N. Sharp.

More on Uses for Wood in the Kitchen: The Beauty of Acacia Wood

4. Your Knife’s Blade Steel Isn’t Up to the Job

The general qualities of blade steel are strength, toughness and hardness. Strength, or edge retention, refers to a knife’s ability to maintain its sharpness during use. For example, cutting cardboard boxes, splintering kindling sticks from larger firewood quarters, or cutting lengths of sisal rope each take a unique toll on the edge of a blade, and the same goes for cutting through different ingredients. Generally speaking, more expensive steels have better edge retention than cheap steels.

A tough blade steel resists chips and total failure when subjected to beating, impact, twisting, and torsion. Tough blade steels are well suited to professional use for extended bouts of food prep on hard surfaces. Where an extremely hard steel would chip, these knives can sustain intense chopping sessions, especially when bones and heavy connective tissue require more force to be applied on the cutting edge.

Frequent encounters with acidic ingredients like citrus, onion and tomato can also damage steel, and certain steels resist rust and corrosion better than others. Types of stainless steel with very high chromium content or exotic power crucible steel can withstand damp and caustic environments with little to no damage. Carbon steels, on the other hand, will pit and rust aggressively in wet environments if not properly cared for. Knives prone to corrosion can be protected with a thin coat of mineral oil.

Maybe one of the most frequently overlooked aspects of blade steel is sharpen-ability. Touching up certain steels with your sharpening stone is an easy, pain-free process whereas harder steels can make for an all-day affair to bring them back to sharp. Being able to field sharpen your knife can be the difference between life and death in the wilderness. An easy to sharpen knife will generally not exhibit excellent edge retention.

The best blade steels exhibit a balance of strength and toughness. Blade steels with an insane amount of hardness (pushing towards 70 HRC) tend to lack stability and can suffer from cracks, chipping and total failure, while extremely tough blades may not cut as well as desired and can suffer from edge rolling and difficulty maintaining an edge – hence why you might have a dull knife.

Knife Knowledge 101: The Anatomy of a Knife (And Why It’s Important)

5. You Don’t Have Time for Regular Knife Sharpening

Even if you follow all the rules perfectly, no knife will stay sharp forever. Every single cut dulls the edge by a tiny, imperceptible amount, and the only way to ensure your knives stay sharp long-term is to keep them regularly sharpened. The problem is, properly sharpening your knives isn’t as easy as it looks, and those home electric sharpeners that lend the promise of saving you time can actually damage and even destroy your knives.

The best option for home sharpening kitchen knives is using a whetstone, and while many professionals swear by their whetstones, properly sharpening a knife is a complicated and time-consuming process that takes a lot of practice to perfect. This makes sense if you work in a restaurant kitchen and need to sharpen your knives on a more regular basis, but for the rest of us it’s simply too much to ask.

How to Keep Your Kitchen Knives Sharp

Keeping your kitchen knives sharp isn’t hard to do. If you take care of your knives and follow the rules of kitchen knife safety, you are one step away from ensuring a lifetime of cutting excellence.

The next step is having your knives sharpened on a regular basis, or about every three to six months, depending on how often you cook. But if you’re not ready to take time to learn how to carefully grind down your knife blade with a whetstone, you can eliminate all of the hassles of knife sharpening by getting F.N. Sharp!

Crafted from premium VG10 steel to reveal a stunning Damascus feather pattern and exceptionally sharp, long-lasting edge, all F.N. Sharp kitchen knives were designed to put an end to dull moments in the kitchen – from the powerhouse chef's knife to the handy little paring knife and even our steak knives, too! Get the whole set or the individual knives you need and you'll be well on your way to staying sharp in the kitchen!

Quality vs. Junk: A Guide to Buying Kitchen Knives