The influence of rheology on sunscreen performance and SPF – Are highly thixtotropic products not providing enough protection?


Formulytica Pty. Ltd., Mulgrave, Victoria, Australia


A sunscreen’s cosmetic attributes have become important as important as its SPF rating. For thixotropic sunscreens developed for pumps, sprays and aerosols their rheology differs widely from the ISO standard 24444. This deviation is proposed as the reason some sunscreens fail to protect the consumer. It is proposed that we should start requiring the rheology of the formula to be tested as well as its SPF performance. If its rheology differs significantly to the ISO standard then the standard is not a valid predictor of SPF protection.

Australia consumers are very sun care aware. The Australian Cancer Council launched the National SunSmart Schools program in 1998 so these pupils have had 20 years of the message of safe sunscreen usage.

In spite of this knowledge there was a spike to 355 people sunburnt in 2017 in Victoria, with 190 people burnt in January alone (See Table 1). This equates to 6 people per day that were sunburnt enough to go to a hospital emergency room rather than just applying a product from a pharmacy for sunburn containing Aloe or Vitamin E at home!

Another worrying trend is that these people were predominately young in the age range of 10-19 year old (while they are the age of beachgoers, they are the ones brought up with the skin cancer message from school age). 

Every summer we see reports of extreme sunburn in the media such as in 2017 when Banana Boat® had multiple sunburn issues with their aerosol products (2). “THE AGE” a respected Melbourne broadsheet, devoted over half of its front page to the issue of sun protection this year (3).

If ...