When Georgia O’Keeffe was alive and painting in the deserts of New Mexico, she noticed white pin-sized blisters forming on the surface of her paintings. She assumed they were bits of sand mixing with the paint. So did many others, even after she died.

But then the bumps, which can form by the thousands, started to grow and spread. Soon after, paint started to flake off. The combination of paint loss and discoloration got people worried.

“Instead of a green surface, what you end up seeing is a green surface with lots of little white dots,” said Dale Kronkright, head of conservation at the Georgia O’Keefe Museum in Santa Fe, New Mexico. “So just the visual impact of our understanding of the painting is changed by the sheer number of these blisters.”

Now, scientists at Northwestern University have diagnosed O’Keeffe’s paintings with something they call “art acne.” It happens when fatty acids in paints mix with lead and zinc pigments also in the paint, creating a metal soap that rises to the surface and creates a tiny bump.

“The problem of soap protrusions in paintings is one of the most critical problems in conservation,” said Marc Walton, one of the scientists who worked on this art acne project. He co-chairs the university’s Center for Scientific Studies in the Arts, a collaboration with the Art Institute of Chicago. “Approximately 70 percent of all paintings have soap protrusions on them.”

At some point, these little bumps can actually pop. That’s when it becomes an art conservator’s nightmare.

“So you have a pock that’s created on the surface of a canvas,” Walton said. “Soaps also can migrate to the surface and form a haze over the painting so it’s obscuring the painting.” All of these, he said, are “unacceptable for the long-term preservation of the work of art.”

Walton and his team aren’t the first to discover art acne on paintings. A conservator in the 1990s was the first to diagnose it on some works by Rembrandt. They’ve been found on art by Johannes Vermeer, Rembrandt van Rijn, John Singer Sargent, Rene Magritte and more. They’re often exacerbated by environmental conditions like humidity or lighting, and when paintings travel frequently.

The problem is most acute with pieces of work created with oil paints before the 1970s. After 1970, manufacturers changed the way they made paint, specifically by adding a dispersing agent called aluminum stearate. Soap protrusions have a harder time forming in the new paint.

Kronkright says the O’Keeffe Museum has such an extensive collection of not just her paintings, but letters where she mentions this issue and the palettes she used during painting.

“It’s just because of this deep, research body of materials that we have at the museum that we’re able to put all the pieces of this puzzle together,” he said.

Right now, it can be a lot of work to diagnose a painting with this acne. Museums must take the painting to a lab for testing. The process involves huge lights and bulky equipment and moving priceless works of art is expensive.

But these scientists developed a hand-held tool that could change all that. It’s a mobile app that can measure the art where it hangs.

“You are armed with data almost immediately so you can make real decisions,” Walton said. “You can go to multiple paintings at the same time to make comparisons … So it changes the way we process data to make it more accessible and more democratically available to people.”

The app uses the display and camera in a smartphone or tablet to create 3D images of the painting, using technology that allows the app to differentiate between a simple brush stroke and one of these bumps of metal soaps. That way, conservators can easily detect issues from their museums, including protrusions that might not be visible to the human eye.

Right now, art acne isn’t completely curable. Conservators can restore paintings, but it can keep coming back. Walton hopes this app can help people better understand how it forms and grows. They hope that might lead to a cure.

“We’re probably around 10 years away from really truly understanding how to do that, and this is part of the process of building the information to be able to understand this microscopic and very complex reactivity that is going on within paint films,” Walton said.

Solving this problem is especially important to a place like the O’Keeffe Museum, where they only show one artist.

“If we were to lose ten percent of what O’Keeffe gave us due to visual color changes or paint loss, that has a significant impact on the life of this museum,” said Kronkright.

The scientists hope to release the app publicly in the next few months. Then, conservators from Santa Fe and beyond can use it to measure art acne, and one day, hopefully find a cure.

Kate McGee covers education for WBEZ. Follow her on Twitter at @WBEZeducation and @McGeeReports.