2.2. Antimutagenic activity and anticancer properties

UV radiation is capable of damaging DNA and therefore participating in cancer pathogenesis through multiple mechanisms such as immunosuppression, oxidative stress, direct DNA damage, inflammatory response, and p53 tumor suppressor gene mutations. On the other hand, it should be taken into account that immunosuppression might be the desired effect in subjects affected by autoimmune diseases [10].

Several methods are available for a predictive in vitro antimutagenic or anticancer activity evaluation, and it is quite difficult to identify a list of preferred tests [11]. However, a good practice should include at least one of the validated methods in the screening of a new substance or mixture [11].

#### 2.3. Anti-inflammatory activity

UV radiation induces the inflammatory response. UVB-induced cyclooxygenase-2 (COX-2) expression leads to an increase in the production of prostaglandin (PG) metabolites. COX-2 expression in the skin has been linked to the pathophysiology of inflammation and cancer. Exposure to UV radiation is also known to increase the expression of pro-inflammatory cytokines like tumor necrosis factor, interleukin (IL)-1, and interleukin IL-6. These antiinflammatory properties including various herbal substances and medicines can be evaluated by a number of methods [12, 13].

#### 2.4. Booster effect

This topic is yet quite complex because it is relatively new and not fully explored. There are already known compounds that can boost the SPF of UV filters [10, 14], but the mechanisms that are responsible for booster effects are heterogeneous and often unpredictable; some are linked to the nature of the UV filter(s) that the formulator wants to enhance. It is, in fact, difficult to uniquely define the general characteristics of an ingredient with booster effect, but it is possible to describe the two main aspects of this topic. The three main strategies available to achieve "booster effect" are interaction with the UV filters at the physical-chemical level to improve efficiency (optimize the efficiency of the UV absorber mixture) [10], implement a correct formulation strategy, and improve the film-forming properties (use of emollients and film-forming agents). One of the reasons of the growing importance of the booster effect is the consolidated marketing trend of placing on the market sunscreen products with higher SPF values; as a consequence of this, the formulator has to find all the possible stratagems to use the smallest possible amount of UV filters in the product. Considering the evaluation of herbal materials as "booster ingredients," this activity is, in some cases, identifiable by the in vitro tests that will be described later. Ingredients that improve UV filter distribution and enhance spreadability are also valuable [15].

According to EU regulation [16], Annex VI reports the list of UV filters allowed in cosmetic products.

List of sunscreen ingredients approved in the USA as presented in the sunscreen drug products for over-the-counter human use monograph" (21 CFR 352.10) [17].
