2. Biological activities connected with solar protection

#### 2.1. Antioxidant and reactive oxygen species scavenging activity

Antioxidant effect represents one of the key mechanisms of photoprotective activity of herbal extracts. The UV skin damage depends also on the generation of reactive oxygen species (ROS). ROS are considered as oxidant agents and are responsible for the development of skin disorders like skin aging, lipid peroxidation, and cancer [6]. These species include hydroxyl radicals, peroxyl radicals, superoxide anion, and, mainly, their active precursors: ozone, hydrogen peroxide, and singlet oxygen. ROS react negatively with DNA, proteins, and unsaturated fatty acids that in turn induce carcinogenic processes and inflammatory response from cells. Phenolic/polyphenolic compounds and flavonoids usually represent the main source of natural antioxidant compounds, and several types of research highlight the usefulness of including natural antioxidant extracts in topical products [6–8].

Antioxidant compounds from herbs offer new possibilities and strategies for an effective prevention and treatment of UV-mediated damages and diseases, which are mainly due to the generation of reactive oxygen species suppressing immune reactions. The benefits of natural antioxidants in topical products are nowadays generally accepted in light of the information available [9]. There are several effective in vitro tests for antioxidant activity. Each of them is based on different mechanisms and, thus, evaluates different kinds of oxidative protection. In order to obtain a sufficient evaluation on in vitro antioxidant, it is thus necessary to perform different types of tests to assess the studied compounds on different kinds of oxidative species.

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

Guidelines for the Development of Herbal-Based Sunscreen

http://dx.doi.org/10.5772/intechopen.72712

47

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

List of sunscreen ingredients approved in the USA as presented in the sunscreen drug prod-

Currently, several in vitro tests for determination of SPF exist. They are all used for screenings performed in the research and developing phase. The first method proposed is the one by Diffey (1989); it is still the most accredited reference [14]. The fundamental characteristic of all the in vitro methods is that they are based on spectrophotometric measurement of the absorbance (calculated from transmittance) of a thin film of product applied on UV transparent substrates. Substrates should be as close as possible to the physical characteristics of the skin.

suitable substrates; they can range from plastic perforated surgical tape such as Transpore™ to

• Transpore™ tape: it is a surgical tape (provided by 3M Health Care Company, Maine, USA). It is used according to the Diffey-Robson's method; this tape has a perforated structure, and it allows the distribution of the sunscreen sample in a way similar to the

• Sand-blasted PMMA plates: this substrate is easy to use and can be supplied with a reproducible roughness. (i.e., Schonberg GmbH, Munich, Germany). The plates have an area of 2 cm<sup>2</sup> and standard roughness of 5 μm. The features of this substrate meet the

Our experience in the research of useful compounds in the solar protection field and an accurate bibliographic research indicate that it is possible to point out several factors and variables which are able to affect the accuracy and the repeatability of the in vitro SPF tests.

standardized plastic plates such as polymethyl methacrylate (PMMA) plates [14]:

recommendation of ISO 24443 for in vitro UVA protection assessment.

. There are different types of

ucts for over-the-counter human use monograph" (21 CFR 352.10) [17].

3. Guidelines for the determination of SPF in vitro

The amount of product applied varies from 0.7 to 2.0 mg cm2

spreadability are also valuable [15].

irregular surface of the skin.

The most important ones are:

• Different compositions of filters • The formulation of the sunscreens

products.

Listed below are some examples of tests that should be carried out to define the whole spectrum of protection. The tests include:

