21st May 2019
In the UK, it is often suggested that the effectiveness of a sunscreen can be judged from its UVA star rating and not necessarily its sun protection factor (SPF), however an SPF50+ sunscreen with 3 stars may actually be more effective than an SPF50 with 5 stars.
The following scientific explanation demonstrates why…
SPF values, which range from low protection (SPF 6-10) to high protection (SPF 50+) provide an approximation of how long it takes for UV radiation to burn skin that has been covered with sunscreen compared to skin that has not.
For example, if skin takes 500 seconds to burn when sunscreen has been applied but only 10 seconds to burn without sunscreen, then the SPF for this product would be 500/10, or 50.
An SPF value must meet a minimum standard to be labelled, so an SPF50+ product must have an SPF value of 60 or above. Conversely, the UVA star rating system provides a value from 0 to 5 on a sunscreen based off the percentage of UVA radiation absorbed by the sunscreen in comparison to UVB. What this means is that a high UVA star value does not necessarily mean that the product provides better protection, it could simply mean that the ratio between UVA and UVB protection is similar (i.e. that the percentage of UVA radiation absorbed by the sunscreen is the same as the UVB absorbed).
SPF and UVA star ratings are both useful indicators of a sunscreen’s effectiveness, but the key to ensuring that your sunscreen will provide the protection it claims is to carefully read the instructions and educate yourself on the rigorous testing that goes into ensuring its effectiveness.
Written by: Dr Fabrizio Spada BSc, PhD, Research and Development Manager at Ego Pharmaceuticals.
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