Science shows that certain smells trigger memories in our brain. For instance, grass may remind you of playing outside as a kid, or freshly baked cinnamon buns could bring flashbacks of working at Cinnabon as a teenager.
Highlighters work the same way! Their chemical smell may just spark memories of being in school. So what exactly is inside of highlighters that gives them their scent? Also, why do they never seem to run out of ink? It’s time for a quick chemistry lesson!
What Ingredients Are in Highlighters?
Most highlighter ink contains fluorescein, which is an organic compound and dye that is soluble in water. The tip, on the other hand, is made from polyethylene or polyester beads, both of which are lightweight types of plastic.
Although most highlighters use fluorescein to get that neon hue, the other ingredients will vary. It just depends on which color is being created.
The following chemicals may be found in highlighter ink:
This chemical compound is primarily used to make yellow highlighters, but surprisingly, it’s also been found in different types of soap!
You can’t go wrong using a highlighter made from triphenylmethane. It will produce a blue ink that stands out in your notes or textbooks.
Rhodamine is a chemical that’s used to dye paper and ink. It’s mixed with triphenylmethane to create pink or purple highlighters.
With its yellowish color, xanthene is an excellent chemical to use in highlighters. It’s mixed with another chemical known as coumarin to create orange ink.
It might be surprising, but coumarin is totally colorless and has a vanilla aroma. This chemical compound is mixed with xanthene to create orange highlighters.
Why Are Highlighters So Bright?
You probably think of the word “fluorescent” when you think of highlighters. This comes from the main ingredient in the ink, fluorescein, which is naturally a lot brighter than other chemical compounds.
Siphon the Plastic
The first step involves siphoning plastic pellets into a large tube. Half of the pellets are white and the other half are dyed in the intended color of the highlighter.
Melt the Plastic
The tube that holds the plastic pellets is heated at about 240°F, which causes them to melt into a liquid form. As it all melts together, the colorful pellets will overpower the white ones, ultimately creating the ink color.
Push Into Molds
A mechanical steel screw pushes the liquid plastic into premade pen molds. The pressure at this point is equal to the weight of 350 elephants!
Cool Down the Highlighters
The highlighter barrels are cooled down by water and stored in a container. Without this step, the highlighters would be too hot to touch and wouldn’t be able to go on to the next stages of manufacturing.
Push in the Polyester
Clear pen barrels are pushed on a conveyor belt, while chalky pieces of polyester drop down on a separate conveyor belt. A robotic arm then pushes the pieces of polyester into the clear pen barrels.
Drop in the Dye
A chemist uses an eyedropper to drop a concentrated amount of dye (usually between 10 and 20 drops) into a beaker of water. This water contains a substance known as a humectant, which allows the ink to retain its moisture. It’s for this reason that highlighters don’t run out of ink very quickly!
Measure the Ink’s Thickness
A metal probe is dipped into the ink. It’s connected to a gauge that measures the thickness of the ink. If the probe turns too fast, it means the ink is too thin. If it’s too slow, the ink is too thick. It has to be moving at just the right speed in order for the ink to be used in the highlighter.
Mix the Ink with the Polyester
A robotically operated needle is used to inject the ink into the chalky polyester pieces from Step Five.
Add the Nib
The tip, or nib, of the highlighter is added to the top of the clear pen barrel. This is where the ink flows out as you’re using the highlighter.
Screw on the Cap
The highlighter caps are moved down a conveyor and added to the top of the nib.
Print a Design
Pack the Highlighters
The highlighters are now good to go. They are packed into boxes and shipped in bulk to stores or online retailers. Demand is usually very high during back-to-school season!
See the entire process in action by watching this video!
How Much Ink is in a Highlighter?
On average, a highlighter will have about 10 ml. (0.33 oz.) of ink. This will give you approximately 50,000 words you can highlight before you have to worry about it drying up. It’s no wonder why it seems like highlighters never go bad!
How Should Highlighters Be Stored?
You should store highlighters upside down with the cap on top. This ensures that the ink won’t dry out quickly, and the highlighter will last for a longer period of time.
The following are great places to store your highlighters:
- Cup or mug on your desk
- Mason jar in your kitchen
- Pencil case that you keep in your bag or backpack
- Junk drawer
- Plastic tub with a lid on top
- Wicker or cloth basket in your office
- Makeshift shelf on a corkboard
Cup or Mug
Keep your highlighters in arm’s reach by storing them in a cup or mug on your desk. Choose a fun pattern or color, and you’ll instantly brighten up your workspace!
If you want to start planning your meals, keep a mason jar full of highlighters and pens in the kitchen. Create a calendar and use one color for breakfast, one for lunch, and one for dinner.
Zippered pencil cases are a great way to keep your highlighters and other supplies organized. You won’t have to sift through the bottom of your backpack again!
Every house should have a junk drawer! This is where you’ll keep odds and ends like rubber bands, pens, scissors, and of course, highlighters.
Plastic Tub With Lid
You might already store your craft supplies in storage containers. Consider doing the same thing for office supplies, such as notebooks, pens, and highlighters.
Wicker or cloth baskets are a must in every household. They look elegant, but also work wonders at hiding any unwanted clutter. Leave a few in your office to hold your highlighters and other supplies!
Create a DIY shelf by pushing two push pins evenly apart on a corkboard. Then you can simply rest your highlighter on the top!
Being organized is said to increase your productivity. With that in mind, it’s worth brainstorming ways to declutter. Start with your office supplies and then go about organizing everything else. You won’t regret it!
Do Highlighters Fade?
Most highlighters will not fade over time! The ink is permanent, which means the mark won’t go away. Keep that in mind if you don’t want to ruin the pages in your favorite novel.
Do you want a highlighter with fade away ink? Try the Fader! This marker features ink that will disappear after just five months. It’s an especially great option for students who want to mark passages in their textbooks without anyone knowing about it!
Are Highlighters Toxic to Humans?
Highlighters are made with chemicals, so it may be dangerous to ingest the ink. If you, your child, or your pet accidentally consumes any toxic materials, reach out to poison control at 1-800-222-1222.
The Bottom Line
Fluorescein, and other chemicals like pyranine and rhodamine, are almost everlasting. Your highlighter marks won’t fade away, even after a few years! So give a silent “thank you” to the folks that make these bright pens. Studying, meal calendars, and projects at work wouldn’t be the same without them!
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Lu, A. (2019, February 14). How Long Does it Take the Average Highlighter to Run Out of Ink? Retrieved from,
How It Works Daily. (2014, July 2). What Makes Highlighter Pens So Bright? Retrieved from,
Smith, S. (2017, February 1). 7 Household Items You’re Better Off Storing Upside Down. Retrieved from,
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