Innovative non-invasive model for assessing antioxidant sun protection in children

UVA rays cause many changes to the skin, including oxidation, which is limited by the squalene found in sebum, a natural antioxidant protector. Children’s skin contains less squalene and is therefore less well protected than adult skin. This is why we have developed a non-invasive in vivo model to assess protection against squalene oxidation and the superficial state of the skin caused by UV rays.

An open-label, intra-individual clinical study was carried out on 10 children aged 4±0 on average, most with phototype II (8). An SPF50+ suncare product was applied for four days to the forehead versus the untreated chin. Superficial samples were taken on D0 and D4 using D-squame^® (in duplicate) combined with pressure monitoring using CuDerm^®. The D-squame samples were stored at -20°C before being exposed to 9 J/cm² of UVA radiation and 300 mJ/cm² of UVB radiation. After extraction and assay by LC/MS, oxidised and non-oxidised squalene were quantified and the ratio of the two was calculated. Scanning electron microscopy (SEM) images were taken for some of the D-squame samples set aside before extraction, to determine a skin surface condition score on D4, inspired by the work of J.W Fluhr (assessment of the presence of more or less homogeneous aggregates reflecting the state of differentiation and the quality of the barrier function).

Irradiation significantly reduced the amount of non-oxidised squalene, thus increasing the oxidised to non-oxidised squalene ratio from 7.0±3.9 to 311.3±208.3 (p<0.01). After applying the SPF50+ suncare product twice a day for four days, this ratio decreased significantly by 19.6% (ratio=251.6; p<0.05) compared with D0. SEM images show the negative impact of UV rays. Better cell preservation was associated with a higher score in the area treated with the product compared with the untreated area (6.2 vs 3.8); the results were similar to the non-irradiated untreated area (6.2 vs 5.5) on D4.