Sunscreen Shenanigans

Beware of false prophets ... ...

I see, as we move into the height of New Zealand’s summer, that several sunscreen manufacturers are again being hauled over the coals by the Commerce Commission for false advertising. The performance of their sunscreens isn’t as good as advertised.

The Commerce Commission were responding to a measurements undertaken by the Consumer Organisation of New Zealand. But the loudest calls for action were from the Cancer Society of New Zealand, who incidentally sponsor and endorse our educational UV-awareness smartphone app (UVNZ, and the older uv2Day app).

The effectiveness of a sunscreen is specified by its Sun Protection Factor (SPF). If a sunscreen’s SPF is 10, its proper use makes the UV exposure time before skin damage ten times as long. Modern sunscreens have SPFs approaching 60. In that case, if the sunscreen is correctly applied, the skin damage after hours of UV exposure would be the same as for only minutes without.

But it’s rare for sunscreens to be correctly applied. The advertised SPF is for an assumed application thickness of 2 milligrams per square centimeter (i.e., 20 grams per square meter). Our body’s skin surface area typically exceeds 1.5 square meters, so for a full body application 30 grams would be required (i.e., about 30 ml, or two tablespoons). Furthermore, sunscreens breakdown with exposure to UV, and they also wear off: several re-applications are needed over the course of a summer’s day outdoors. So keeping safe becomes rather expensive, especially given that the cost per litre of sunscreens is the same as whisky.

Years before this last scandal, I was involved in another sunscreen scam where manufacturers were advertising “all-day-protection” for their sunscreens, implying that a single daily application would prevent skin damage. When the Cancer Society questioned the claim, the Commerce Commission asked me to help. It turned out to be easy to debunk. The sunscreens involved were advertised as having an SPF of 30, but the cumulative dose of UV over a summer’s day so much that a larger SPF would be required for all-day-protection.

Even in the lower South Island of New Zealand (e.g., Lauder, Central Otago), where there’s significantly less UV than in the north of the country, the daily UV dose can exceed 75 SED (SED, is an abbreviation for Standard Erythemal* Dose, where 1 SED is 100 j/m2 of sunburning UV). So, even using a correctly applied sunscreen with an SPF of 30, the dose would exceed 75/30 = 2.5 SED. But, for the most sensitive skin types (e.g., of Celtic origin, pale skin, with blue eyes and red hair), damage can occur for less than that.

Therefore, even if the sunscreen were applied correctly, and assuming no solar degradation in performance (neither of which is true in practice), skin damage would still occur for the most at-risk skin type (i.e., the people who most need accurate advice). As a result of my report, submitted to the Commerce Commission in November 2007, the sunscreen manufacturers had to change their advertising.

Not just another gratuitous dolly-bird sunburn picture on the beach. This one shows my colleague Martin Allen’s hand holding up one of his personal UV dosimeters to screen the sun from the camera lens.

In an odd coincidence, the Cancer Society’s own sunscreen  (along with 8 other products from a sample of 20 tested by New Zealand’s Consumer Organisation) was taken to task in 2019 because its SPF was lower than advertised. It’s a timely reminder to make sure your own house in order before criticizing others.

They’ve now fixed the problem, and I agree with them that sunscreens should be properly regulated, especially here in the skin cancer capital of the world. They should also be more affordable. Perhaps there’s a role here for Pharmac?

* Erythema = Skin Reddening = The first detectable sign of skin damage from UV exposure

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