Development of actinic lentigines due to multiple sub-erythemal exposure to UVA1 radiation in Asian skin.

The appearance of actinic lentigines mainly found on face, back of the hands, upper back and décolleté is associated with chronic sun exposure. However, there is no study looking at the role of long UVA specifically in the development of actinic lentigines. This study was conducted in 20 Japanese adult women exposed on the upper back area three times per week for 6 weeks to incremental sub-erythemal UVA1 doses (5 J/cm2 at weeks 1 and 2, 10 J/cm2 at weeks 3 and 4 and 15 J/cm2 at weeks 5 and 6). Clinical assessment, performed on day 0 (before any exposure), and on days 14, 28 and 42, included the evaluation of skin pigmentation (pigmented spots), chromametry of the pigmented skin lesions and measurement of dyschromy. The number of pigmented spots and uniformity of the skin's pigmentation were clearly increased in comparison with baseline, statistical significance of the difference (p < 0.05) being reached at D 28 and D 42 in both cases. In conclusion, repeated sub-erythemal UVA1 exposure induces the development of actinic lentigines. Thus, a suitable protection including long UVA coverage is also needed to prevent from the damages induced by low, sub-erythemal doses of UV exposure.