I was never very good in the hard sciences, yet I spent an afternoon in a Honolulu Community College classroom staring intently at some numbers on the chalkboard, trying to make sense of the results of students’ sunscreen readings.

Without lab access, consumers are often forced to rely on efficacy claims made by cosmetics manufacturers. Over the years we’ve watched SPF (sun protection factor) numbers climb from 15 to 60-plus. Meanwhile, consumer protection advocates have said claims of SPF numbers exceeding 30 are probably false.

Whom are we supposed to trust?

So, when professor Michael Ferguson e-mailed to say his chemistry class was testing sunscreens and would I like to visit the lab, I was there, with some of my own expensive versions.

As I do with all my other makeup and skin care, I take a Russian roulette approach to sunscreen, using multiple brands at once because I’m not sure what really works. I was also interested in testing the SPF of my mineral makeup. Mineral brands tout the sun-protection capabilities of their products, but I wasn’t sure these powders offered the protection of creams and I don’t know how much to use to be protected.

The chemistry class is required of students in the school’s cosmetology program and is geared toward their areas of expertise and concern.

"When they get out of school, they’re going to be working with lots of strong chemicals that are not just damaging to hair, but to their skin," Ferguson said. "It’s an occupational safety concern, so I try to give them information that’s going to be applicable to their jobs."

During the semester, students spend some time making soap and learning about various chemicals in hair products, such as plasticizers in styling gels that dissolve in alcohol but dry to give hair a hard, spiky look. The plastic is low in toxicity in the hair, Ferguson said, but it washes out and spreads everywhere, posing a threat to the environment. Certain plastics have been shown to interfere with the reproductive systems of animals.

In comparison with working in a salon, Ferguson said, being a chemist is a very safe job. "We have the knowledge of ingredients and proper procedures to protect ourselves. If I’m working with hazardous chemicals, I’m going to be wearing gloves, a coat and goggles."

Salon employees don’t have that advantage. To don that much protective apparel would scare customers, and while Ferguson said the typical salon client need not worry much about the few dozen annual encounters with products that have been marketed for years, salon employees sometimes suffer from the cumulative effects of breathing in fumes and handling chemicals 40 hours a week over a working lifetime.

During the sunscreen class, Ferguson had his own collection of sunscreens to demonstrate the difference between SPF claims and tested numbers, and invited students to bring in their own products as well.

Manaka Kojima, Ye Eun Park and Janell Celestino took him up on the offer.

Kojima was eager to test a sunscreen she bought while visiting Japan. Its name, Sun Killer with SPF 50+, held promise.

Park entrusted her Clarins UV Plus SPF 40 with keeping her skin smooth and clear, and Janell Celestino believed her Miami Ink SPF 50, thick enough to cover tattoos, would be powerful enough to ward off the sun’s UVA (wrinkle causing) and UVB (sunburn) rays.

Students rubbed the sunscreens on sheets of plastic wrap to approximate a thin layer on skin. The wrap was then held in bright sunlight, over a digital probe connected to a computer, to show how much UVA and UVB were being blocked.

Surprise!

None registered more than SPF 8.

The students expressed their disappointment. Park, who moved here from Korea three years ago, said that in that time she noticed her skin "totally changed."

"I have a lot of wrinkles and spots I never had before," she said.

When her Clarins SPF 40 sunscreen tested at 8, she said: "I’m not going to use this anymore. I’m so disappointed."

Kojima, too, said it wasn’t worth bringing Sun Killer back from Japan, although it outperformed all but two brands in blocking UVA rays. Miami Ink performed best.

Before you ditch your SPF 8s, the number is not so bad: SPF is measured on a logarithmic scale, so SPF 2 blocks 50 percent of the sun’s rays, and SPF 4 blocks another 50 percent of that, for a total of 75 percent sun-blocking power. SPF 8 blocks 87.5 percent of the sun’s rays, leaving just 12.5 percent squeaking through. And it doesn’t get much better than 30 SPF, which blocks about 96 percent of sun’s damaging rays. Beyond that, wear a hat or just stay indoors.

Even so, to attract consumers, nearly 1 in 6 products now lists SPF values higher than 50, according to the Environmental Watch Group.

As for the luxury brands, it was good to know that ZO Skin Health’s Oclipse SPF 30 Sunscreen + Primer lived up to the claim of its founder, Dr. Zein Obagi, and Kate Somerville’s Protect Serum Sunscreen matched that number, although it was billed as SPF 55.

Just a light film of mineral sunscreens also offered SPF 8 protection.

And while I was relieved to learn mineral sunscreens do live up to sunscreen claims, the International Agency for Research on Cancer is reporting that inhaling loose particles of zinc and titanium dioxide, ingredients often found in mineral sunscreens, is possibly carcinogenic to humans.

The studies will continue. In the meantime, if you’re using mineral sunscreen, hold your breath while applying.