The laundry detergent aisle of every U.S. grocery store is home to a shining example of the huge impact the smallest innovations can have, and what happens when there seems to be no incentive to be innovative.

The measuring caps on liquid laundry detergent containers are universally difficult to read, because of faint markings that blend in with the plastic cups. Without perfect lighting conditions and sharp vision, this has left many consumers squinting to see where the line is that they should fill to. And the related instructions are often vague.

As a result, consumers are left to over-pour detergent, sending money to the pockets of the flawed caps’ creators.

Laundry detergent is a $6.95 billion industry in the United States, and liquid detergents make up 75 percent of sales, according to research firm Nielsen. The average American household spends $37.52 a year on laundry detergent. Although it is impossible to pinpoint exactly how much detergent is wasted, experts say a significant portion of the industry’s revenue comes from excess use of detergent that consumers didn’t need to use to clean their clothes.

“From a usability standpoint, they are kind of a failure,” Andrea Ruggiero, an industrial designer and professor at the New School, said of the caps. “It’s a generally wasteful practice.” He recommended that companies add clear markings that suggest using slightly less detergent than what is required, because consumers tend to overfill, thinking that makes their clothes cleaner.

But laundry detergent companies lack an incentive to do just that, Ruggiero said.  The more detergent consumers use, the more money the companies make.

When asked whether the monetary incentive claim was true, a spokeswoman at Procter & Gamble, which sells detergent brands such as Tide, Cheer and Gain, said the company strives for continued improvement and ways to make its products better.

Experts say a good measuring cap is doable all that’s needed is a contrasting color to mark the lines consumers should fill to. Pyrex realized this back in 1942 when it debuted a clear glass cup with horizontal red lines that is now commonplace in many kitchens.

Yet laundry detergent companies stick with a design that has its roots in the 1930s, when a patent was issued for a measuring top for containers. Since then, the form of the bottles has improved very gradually over the decades, with the addition of spouts designed to ease pouring and a feature to channel excess drip back inside to the bottle, rather than splattering on the exterior.

And instructions for how to fill the caps today offer a lot of leeway. Almost none even offer guidance for a small load. But it just so happens that consumers left to customize will over-use detergent.

Jeff Liebel, who worked as a sales representative for Tide parent company Procter & Gamble as it introduced liquid detergent in the 1980s and who now owns a management consulting firm, recalls an understanding that consumers left to their own devices are awful at portion control.

“It would be desirous on the part of the manufacturers to make it a little harder to see [the cups] because you’re not going to underestimate, you’re going to overestimate,” he said, citing research that was passed on from Procter & Gamble product managers. “The measurements are in the cup, so we’re doing our duty to help you as best we can. So pat ourselves on the back for doing that, we’re good guys and all, but, quite frankly, we don’t care.”

One of the most egregious example of a difficult-to-use measuring cap is Purex. Its detergent caps have eight different lines faintly marked on the inside of the lid — 0, 1, 2, A, B, C, D and E. But consumers are only instructed to fill to a single line for regular loads, and “use more for heavily soiled or large loads.” It’s unclear when and if the other seven lines should be used. Purex did not respond to multiple requests for comment.

Xtra, All and Wisk all sell detergent with grooves on the outside of the caps, which cast shadows on the interior, making it even more challenging to see the already faint markings.

“I’m young and blessed with healthy eyesight, and sometimes even I have to squint and struggle,” said Olga Saratova, a self-identified “laundry nerd” who blogs on the subject. “The markings inside the cap are so difficult to see that you just don’t bother, and you’re like, I’m going to guesstimate maybe it’s a half cap a load, when really your line 1 is much less than half a cap.”

Saratova said, in a perfect world, contrasting lines should be on the outside and inside to help consumers measure properly. Instead of taking such an approach, detergent companies have delivered minor tweaks.

Seventh Generation, for example, switched from opaque white caps to translucent caps in 2008 to aid consumers after receiving questions about finding the proper measurement. It considered different color lines on its caps but said this would add a secondary step and require a new mold, which would increase its cost.

Tide changed its measuring caps in 2015 to vertical bars instead of horizontal rings because it said consumers found them easier to read. A spokeswoman could not determine if the company had ever looked at using a contrasting color to aid the caps’ readability.

Total Home, a CVS brand, has five different measuring lines. Instructions call for using the second line for regular loads, and to “use more for large or heavily soiled loads.” A CVS spokeswoman said the four unexplained lines exist for consumers to customize their use based on load size. 

For the foreseeable future, consumers struggling to find the perfect detergent dose for their laundry will have to keep making do.

“It’s 2016,” said Matthew Bird, assistant professor at the Rhode Island School of Design. “We should have this fixed.”