DERMSCAN: AGING VERSUS PHOTOAGING

20 January 2017

Direct link to the Dermscan publication…

Cutaneous aging is a complex and multifactorial process; it implies both structural, functional and aesthetic changes happening at a variable rate.

Recently, Krutmann and his colleagues defined the concept of “skin aging exposome” . It consists of “external and internal factors and their interactions, affecting a human individual from conception to death as well as the response of the human body to these factors that lead to biological and clinical signs of skin aging”. Sun radiations (ultraviolet UV, visible VIS, infra-red IR) are one of these environmental factors.

The impact of UV radiations on skin has long been studied. Already in 1969, Pr. Kligman evoqued their additional role in aging [3] and coined to the term “photoaging” to describe changes that develop after many years of cutaneous exposure to non-extreme, low doses of UV radiations [4]. One of the best-known example of “photoaging” is illustrated in figure 1, showing a 69-year-old man with unilateral dermatoheliosis (another term for photoaging) [5]. This man reported that he had driven a delivery truck for 28 years. Chronic UVA exposure, transmitted through window glass, resulted in the progressive thickening and wrinkling of the skin on the left side of his face.

Although we know, now, that VIS and IR radiations also have deleterious effects, the term “photoaging” still refer to chronic UV exposure. A randomized, controlled study conducted by the National Health & Medical Research Council of Australia for 4 years over more than 900 subjects demonstrated that daily sunscreen application (with UV filters) can specifically delay photoaging signs .

Figure 1: Unilateral dermatoheliosis due to a 28-year-history of car driving .

PHOTOAGING: BIOLOGICAL EFFECTS AND CLINICAL SIGNS

Face, neck, chest and the back of the hands are the areas most affected by photoaging since they are UV-exposed nearly all year long. 80% of facial skin aging is attributed to UV-exposure .

At the physiological level, UV radiations amplify several mechanisms :

While intrinsic aging corresponds to a thinned epidermis and fine wrinkles, the photoaged phenotype is characterized by fine and coarse wrinkles, skin dryness, skin laxity, pigmentation and vascular abnormalities (lentigines and telangiectasia respectively), sallow color and rough texture [9]. Histologically, the deposition of elastotic materials in the dermal connective tissue has long been considered a hallmark of photodamage (=solar elastosis) since it was found to correlate to the quantity of UV radiation received by the skin [10]. Endogenous protection systems (DNA repair systems, antioxidant defense, etc.) present in the skin influence the susceptibility toward photoaging [2]. Age groups or ethnic groups – due to different skin pigmentation – may therefore present different clinical signs of photoaging [11].

Objective and reliable characterization of the degree of photodamage is important to evaluate the effect of treatments. Various clinical scores and grading systems have been proposed, accompanied or not of representative photographs: the SCINEXA [12], the Griffiths’ score [13], the Larnier’s score [14], the Glogau’s scale [15], etc. To date, there is no “gold standard” to assess photoaging [16-19]. Numerous non-invasive technologies can be useful to complete the clinical evaluation [20-25].

SOME INSIGHTFUL APPROACHES PROPOSED AT DERMSCAN TO EVALUATE PHOTOAGING

Photoaging management can be either preventive (e.g. sunscreen against UV damages) or curative (cosmetics to help reduce skin damages). In order to demonstrate the activity of your products on such process, long term studies must be conducted (at least 3 months). Thanks to our facility in Tunisia and our partner in Mauritius, we can also offer studies in sunny environments.

Depending on the activity of your product, multiple approaches can be combined to demonstrate its efficacy.