Sunscreens

We’ve come under fire from industry for taking this approach. We asked industry group Cosmetics New Zealand for scientific evidence that decanting samples in this way compromises the results. It told us its main concern is with product stability during this process.

The expert advice we’ve received, as well as information from the accredited labs that undertake our testing, have confirmed there is no detriment to decanting products.

Our accredited labs tested the sunscreens following the methods in the Australian and New Zealand standard AS/NZS 2604:2012.

We test against two aspects of the standard: a sunscreen’s SPF (sun protection factor), which measures protection against UVB rays, and its broad-spectrum protection (against UVA and UVB rays).

SPF testing

The standard requires SPF to be assessed using a test panel of 10 volunteers in a lab. Testing on humans determines a sunscreen’s ability to provide protection and stay on the skin without breaking down.

The sunscreen is applied to a test subject at a rate of 2mg per cm2 skin. The sunscreen is evenly spread and allowed to dry for 15 minutes. A similar-sized area is measured out and left unprotected.

A special lamp, simulating the part of the UV spectrum that causes sunburn, is shone on both areas for varying amounts of time. The next day a technician determines the smallest dose of UV light required to cause redness in both areas and this is used to determine the SPF. The SPF results are averaged across the 10 volunteers.

Broad-spectrum protection

Using a spectrophotometer, the lab measures the UVA protection passing through a thin film of sunscreen on a plate. To pass, a sunscreen must meet two requirements. It has to reach a “critical wavelength”, which ensures UVA protection extends to wavelengths that penetrate deeper into the skin, and its protection against UVA must be at least a third of the SPF protection against sunburn.