Are Sunscreens Useful in Photodamaged Skin ?

Photoaging is the consequence of cumulative sunexposure and manifests among other features as premature wrinkling, pigmentation changes and presents histologically as solar elastosis

It is generally accepted that when the Ultraviolet threshold has been received, DNA is irreversibly damaged which results in the phenotype

The authors have previously demonstrated the positive long-term application of sunscreen in suppressing Actinic keratosis (AK)
The following study measures the effect of sunscreens on the prevention of signs of photoaging: dry coarse skin, spots, solar elastosis
Generally speaking, patients who have precancerous and cancerous skin conditions are advised to wear sunscreen and sunprotective measures in the hope new lesions will be preventive.

In this study, Sunscreen was applied daily by 14 Japanese elderly people:
-7 males and 7 females (mean age 79.6 years old, range 69-91)
-Sunprotection factor (SPF) was 30

Measurement before and after the study
–Water content (skin surface hydration), Transepidermal Water Loss (TEWL), number of spots, number of wrinkles, skin texture

–Results:
1. only skin surface hydration increased in a statistically significant way.
2. erythema and texture improved in all patients
3. All patients continued to have solar elastosis and it got worse 1 patient

Sunscreen usage varied greatly among the participants over the 18month study period:
sunscreen usage was measured by water content along with that of skin texture and number of spots

Conclusion: there was increase in the number of skin lesions and number of spots if no sunscreen was applied for 18 months. A 20g per day use would result in no increase in the number of lesions.

Our Comments
This study still raises questions:
-do skin lesions continue to appear when a threshold of cumulative sundamage is reached or do new lesions continue to appear ?
-a larger prospective study would be required

In other words, This study shows that new lesions can nevertheless continue to appear despite this and one can wonder if new lesions are the result of:
–additional ultraviolet light absorbed by the skin in unprotected areas when the patients feel protected (such as under an umbrella when walking in the sun)
-an effect independent from additional UV light (used up sun capital = threshold of cumulative sundamage)
-an effect of electromagnetic rays not filtered by sunscreen (infrared light, visible light)

Take home message
-prevention of lesions is better than curing them
-preventing new lesions from appearing can be reduced by sun avoidance (staying in the shade, wearing a hat…). Sunscreens are part of sun protective techniques but not a panacea

Contributors:
Dr Christophe HSU – dermatologist. Geneva, Switzerland
Source of information: Mizuno M. et al. P12-17 [O3-22] The effects of continuous application of sunscreen on photoaged skin in Japanese elderly people the relationship with the usage. JSID Annual Meeting (Japanese Society of Investigative Dermatology, 日本研究皮膚科学会) 2015 – Okayama, Japan