Companies know science sells so they try to drop in respectable-sounding phrases without falling foul of fair trading laws.

University of Auckland consumer behaviour lecturer Dr Denise Conroy says using scientific terms, such as “restoration” or “cell strengthening”, is a “way of positioning things as being good for our health – that by buying these products we’re doing something for our health, not our vanity”.

Skincare companies typically describe less-robust evaluations as “clinical tests”, “clinical studies”, or stand-alone “trials”.

A better term to look for is “clinical trial”. Only a robust gold-standard clinical trial can prove a product will have any effect on your skin, Dr Scott-Lang says.

This Latin phrase translates as “in glass” and means the tests were done in a tube or dish containing human skin cells.

However, your skin acts a barrier, and has evolved to keep things out.

So while the product could theoretically have an effect on your cells once it gets in, an in vitro test doesn’t tell you whether the product will actually make it into your skin in the first place. Instead, look for trials where people have applied a product to their skin and had their lines and wrinkles measured before and after.

These tests typically ask every member of a group to use a product and report on any improvements they see.

However, if you’ve spent weeks applying a cream and want the product to work, you’re psychologically primed to see a positive effect.

Dr Conroy says an unconscious desire to reciprocate may also influence participants. “If we get something expensive for free, we’re much more likely to be positive,” she says.

The best trials use objective measurements instead of self-evaluation — for example, measuring the depth of a specific wrinkle before and after. Ads rarely get into this sort of detail — we needed to request test results from companies to find out.

This is simply too small a test group to determine what might work for all consumers, Dr Scott-Lang says. We found companies may use just a handful of people in tests.

The smaller the group, the more sceptical you should be. Conversely, a test group of a few hundred people can tell researchers not only if the product works but how big an effect it has, provided the study is well-designed.

Customers may not be terribly keen to blow hundreds of dollars on a product with a confirmed but only modest or short-term effect on the skin.

“The general consensus is there’s not enough evidence to support the claims of many of these products,” Dr Scott-Lang says.

Many of us have heard of the placebo effect. By randomly giving half the participants a sham product that looks just like the real thing, skincare manufacturers can test whether their product delivers on their claims. If the ad doesn’t mention a placebo, it’s safe to assume the tests didn’t use one.

Don’t panic — by blind or double-blind, researchers typically mean both the testers and the test subjects have no idea which is the real cream and which is the placebo. This means researchers and test subjects can’t unconsciously favour the real product. However, we’ve seen the term used by some companies to describe tests without placebos, which risks misleading consumers.

Any clinical trial published in an independent, reputable journal is scrutinised by other experts who will highlight flaws. It also means you can read the results for yourself.

Most skincare companies we asked provided their test results — though a couple were a bit selective. By requesting this information, we could tell whether the evaluation met good scientific standards and if the company tested the actual end product they sold on the shelves — some rely on tests on a single ingredient in the cream

Answer: The effects of the serum may be temporary.
Why: Any decent moisturiser will boost the water content of your skin, which will temporarily disguise fine lines and wrinkles.

Answer: False.
Why: The skin is a barrier and has evolved to keep things out. Even the tiniest particles may not cross through the skin’s outer layers. Therefore, skincare companies need to determine which ingredients in their products the skin does absorb and which it doesn’t.

Answer: A test where the product is added to skin cells kept alive in a dish.
Why: “In vitro” is a Latin phrase and translates as “in glass”. It means the product has been tested in the lab but not on a real person.

Answer: They don’t provide good evidence the product is absorbed into the skin, and so aren’t a reliable indicator it will improve your skin.
Why: Dermatologists advise consumers to look for tests where a product has been applied to a person’s skin, and their wrinkles measured before and after.

Answer: Half the participants in the research were give a fake product to use during the 6 weeks, while the rest used the real thing. Everyone was tested to see if their lines and wrinkles had improved. The anti-wrinkle cream performed better than the fake product.
Why: The placebo effect was first discovered in the 18th century. Researchers know a fake treatment (such as a sugar pill) can significantly alleviate symptoms. To demonstrate a product’s efficacy, it must significantly outperform a placebo — in the case of skincare, a fake cream.

Answer: False.
Why: These tests ask people to use a product and then survey them on any improvements they see. Self-assessments are subjective and participants may be primed to see positive effects that aren’t really there.

Answer: A trial with 300 people.
Why: A trial with 10 people is too small to determine what might work for all consumers, so studies of this size deserve your scepticism. A trial of 30 people would be an improvement, but is still relatively small. Conversely, a group of 300 is large enough to give you some confidence in the results, provided the trial is well-designed. Several trials showing consistent results would be even better.

Answer: None of the above.
Why: There are no standard definitions for claims such as “dermatologically tested” or “hypoallergenic” and they don’t mean much. Products carrying these claims may also contain ingredients, such as fragrances and preservatives, which can cause allergic reactions in some people.

Answer: None of the above.
Why: Cosmetics are required to comply with the Cosmetic Products Group Standard, administered by the Environmental Protection Authority (EPA). The standard prohibits the use of certain ingredients and sets limits on the use of others. But the EPA doesn’t test products before they arrive on shop shelves.