Formulation of Emulsions with Photoprotective Action

MITITELU Magdalena1, OPREA Eliza2*, UDEANU Denisa Ioana4, DINU-PÎRVU Cristina-Elena3, GHICA Mihaela Violeta3, OZON Emma Adriana4, PRISADA Răzvan Mihai3, IONIȚĂ Ana Corina1, HÎRJĂU Mircea4 

1Clinical Laboratory and Food Safety Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)

2* Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of Bucharest, 4-12 Regina Elisabeta, 030018, Bucharest (ROMANIA)

3Physical and Colloidal Chemistry Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)

4Pharmaceutical Technology Department, Faculty of Pharmacy, ”Carol Davila” University of Medicine and Pharmacy, 6, Traian Vuia Street, 020956, Bucharest (ROMANIA)

*corresponding author: eliza.oprea@g.unibuc.ro

Abstract

It is well known that due to the lowered ozone layer, a consequence to the rising level of global pollution, sunlight and specifically ultraviolet rays are becoming more and more dangerous to the skin which is the protective surface of the body. For this reason, numerous cosmetic products contain sunlight protection filters. In this work, some photoprotective cosmetic emulsions with a sunlight protection filter, octyl methoxy cinnamate, and vegetal oils were prepared. The emulsions obtained were analysed according to the present standards in order to determine their stability and efficiency.

Keywords: photoprotective cosmetic emulsions, octyl methoxy cinnamate, photoprotection index

Introduction

      Although the presence of the sun is essential for human beings and has beneficial effects, such as synthesis of vitamin D, amelioration of certain dermatological diseases (psoriasis, atopic dermatitis, vitiligo), mental health, an excessive sun exposure carries many risks and can cause serious illness. Ultraviolet radiation is the main etiological factor in the development of skin cancer. Depending on the wavelength, expressed in nanometers, the ultraviolet region (UV) can be divided in Vacuum UV (100-200 nm) and near-UV. The near-UV region includes UVC (200-290 nm) blocked by the ozone layer, respectively UVB (290-320 nm) and UVA (320-400 nm), both penetrating the atmosphere and affecting the human body [1,2]. UVB rays are stronger than UVA rays. They can affect the skin’s cellular DNA, but are also responsible for sunburn. Moreover, they can also cause skin cancer. Sunburn (inflammation/erythema) is a toxic, inflammatory reaction on the skin, produced by UVB radiation, showing the classic signs of inflammation such as redness, heat, pain and edema [3,4]. Limited exposure to UVB radiation stimulates the production of melanin, which causes the gradual installation of a long-lasting tan. UVB also stimulates the production of cells that thicken the skin, which means that it gains increased resistance to radiation. Excessive and unprotected exposure of the skin to sunlight can cause premature aging, depigmentation and even skin cancers [5,6].

      Most UVB rays (85%) are stopped by the first layer of skin (epidermis) and only 15% reach deeper into the dermis. Their value depends on the season, altitude and exposure hour. UVB rays are responsible for the tanned appearance and sunburn. In the long run, the body’s exposure to UVB can have a carcinogenic effect [7].

       Thus, nowadays, numerous cosmetic products like lipsticks, skin care creams, body lotions, hand care creams, shampoos etc. contain sunlight protection filters. These products are designed for persons who do not expose themselves to sunlight as a leisure activity, to whom products with sun protection factor are recommended. Sunscreen testing requires a UV-Vis spectrophotometer fitted with a procedure compliant integrating sphere accessory, and this system is required to meet the photometric linearity range stated by COLIPA [8].

The products containing photoprotective agents are recommended in:

• preventing photosensitive dermathosis;
• preventing drug phototoxicity (in case of drugs with photodinamic potential like: tranquillisers, antihistamines, analgesics, antibiotics etc.);
• protection in case of sun exposure in regions with strong sun radiation;
• protection of persons with hypersensitive skin.

The sun protection factor index is the unit that measures the protection offered to the skin against UVB radiation, not UVA radiation [9]. In order for the skin to be protected from both types of radiation, a sunscreen product with “broad spectrum protection” must be used.

     Foods rich in antioxidants, such as fruits and vegetables, as well as foods with anti-inflammatory potential are particularly effective in counteracting the effects of UV radiation. Exposure to UV rays stimulates oxidative stress caused by free radicals, which means that the skin aging process is promoted by this solar radiation [10,11]. But a healthy diet, rich in nutrients with antioxidant action, has the ability to cancel the effects of free radicals. Therefore, especially during the summer it is recommended to adopt a diet rich in fruits, vegetables, fish, seafood and whole grains [12-16].

      In the experimental part of this work, some photoprotective cosmetic emulsions with a sunlight protection filter (octyl methoxy cinnamate) were prepared and characterized.

Materials and Methods

      Usually, when preparing dermato-cosmetic creams, it is recommended to combine vegetable oils rich in fat-soluble vitamins and poly-unsaturated fatty acids for their emollient, moisturizing, regenerating and nourishing effect.

In the photoprotective creams formulation the following compounds were included:

• a sunscreen: octyl methoxy cinnamate which absorbs the radiation from UVB region (280-340 nm). The substance has a good skin tolerance and a photoprotection index around of 10. It also has a good absorbency at 305 nm and is insoluble in water, so it is recommended for water proof preparations. The researches have emphasised a 5-18% decrease in activity under light action when the substance is dissolved in liquid paraffin or isopropyl myristate. So, the authors have considered necessary to use higher concentrations (5-18%) and to include other, more stable, sun protector agents, in the formulation [8]. In addition, the substance is included on list of sun filters admitted by European legislation (COLIPA Directive; c% max. admitted: 10) [9];
• olive oil with emollient action and absorption in UVB domain, very used in cosmetic preparations; olive oil has been used since ancient times as a protection against the sun’s rays. It protects the skin, moisturizes it and at the same time emparts a pleasat colour to the preparation;
• sweet almond oil which consists chiefly of oleic acid, with a small proportion of the glyceride of linoleic acid and other glycerides, but contains no stearin. It is thus very similar in composition to olive oil (for which it may be used as a pleasant substitute), but it is devoid of chlorophyll, and usually contains a somewhat larger proportion of oleic acid that olive oil [17]. It has also a small absorption in UVB domain; sweet almond oil is obtained by mechanical pressing of the selected and subsequently filtered almond kernels. It has a superior nutritional efficiency, being rich in vitamins (A, B and E), minerals and important fatty acids (oleic acid, linoleic acid):
• calendula tincture with regenerative and antimicrobial action. It favours the burns recovery and has soothing, decongestant and hydrating action; is a hydroalcoholic solution obtained by cold extraction from the flowers of the Calendula officinalis plant.
• an antimicrobial preservative solution, which contains methyl paraben and propyl paraben (3:1 w/w) in concentration of 0.1% [18].

The photoprotective emulsions were prepared according to formulas presented in Table 1.

Table 1. Photoprotective emulsions composition 

Component	Formula A	Formula B	Formula C	Formula D
octyl methoxy cinnamate (g)	5	5	7	7
almond oil (g)	34	–	20	–
olive oil (g)	–	45	25	30
wax (g)	3	2	–	2
lanolin (g)	–	5	10	–
cholesterol (g)	–	3	3	–
Span 60 (g)	2	–	–	2
Twin 80 (g)	3.5	–	–	3.5
glycerine (g)	–	–	–	10
calendula tincture (g)	7	5	5	7
preservative solution (g)	ad 100	ad 100	ad 100	ad 100

The formulas A and D represent oil/water emulsions, stabilised by the emulsifier pair Span 60 – Tween 80. The others formulas (B and C) represent water/oil emulsions, stabilised by the emulsifier pair cholesterol – lanolin.

        The emulsions prepared were subjected to control tests in order to determine their characteristics, stability and efficiency:

• the determination of the appearance was performed by visual examination with the magnifying glass (4.5x) of a sample stretched to a thin layer on a microscopic blade;
• the determination of the main characteristics was made according to Romanian Pharmacopoeia Xth edition [18];
• the determination of the emulsion type was made by following tests: dilution, colour and electrical conductibility [19,20];
• pH was determined after the ointment sample was suitably processed, respectively after the extraction of a hydrophilic sample with water (1:5), followed by the measuring of the pH of aqueous phase, as follows: 25 mL of distilled water were added to 5g sample and the mixture was stirred into an Erlenmeyer glass with cork heating on the water bath at 60°C for 10 minutes. After cooling, the watery phase was separated by the oily phase, and on watery phase the pH was determined with Radelkis pH-meter;
• the determination of relative density was made with picnometer [20];
• the determination of the viscosity was performed with a rotational Brookfield LFV viscometer [18,20];
• the determination of the stability was carried out by maintaining the samples at two temperature conditions (2°C and 40°C): into a weighing ampoule with lid 5g of sample were introduced and the ampoule is maintained 8 hours at mentioned temperatures. Then, the appearance of sample was examined;

      The spectral characteristics of the sun filter and vegetable oils (separated and in sun filter : oil equal parts mixture) were also studied using a spectrophotometer UV-VIS Cecil 2501.

Results and Discussions

      The spectral characteristics of the filter and vegetal oils used for the emulsions preparation are presented in Fig. 1-5. 

 

Fig. 1 Spectral characteristics of sunscreen

Fig. 2 Spectral characteristics of olive oil

Fig. 3 Spectral characteristics of sweet almond oil

Fig. 4 Spectral characteristics of mixture sunscreen : olive oil 1 : 1

Fig. 5 Spectral characteristics of mixture sunscreen : almond oil 1 : 1

The figures above show that vegetal oils analysed absorb in UVB domain (especially olive oil) and the filter has an absorption band between 270-335 nm (λmax = 300nm). In mixture with vegetal oil, the filter absorption was slightly modified, and a very small shifting towards rising wave lengths can be observed.  

According to the UV absorption spectra, a better absorption of olive oil is recorded in the UVB field compared to sweet almond oil; also the mixture of sunscreen and olive oil showed a better absorption in the UVB field. The sun protection index is expected to be better for creams prepared with olive oil.

The characteristics of the emulsions prepared are presented in Table 2.

Table 2. The emulsions characteristics

Characteristics	Formula A	Formula B	Formula C	Formula D
macroscopic characteristics	homogenous; colour: white-yellowish	homogenous; colour: white-yellowish	homogenous; colour: white-yellowish	homogenous; colour: white-yellowish
emulsion type	oil/water	water/oil	water/oil	oil/water
pH	5.7	6	6.2	6.5
viscosity (cP)	203	214	212	198
relative density	0.97	1.09	1.02	0.93

 The data from Table 2 show that the emulsions are homogenous, with pH values close to the skin pH. Moreover, the preparations have presented a good stability by maintaining the homogenous appearance at 2°C and 40°C.

Conclusions

        The experimental photoprotective cosmetic emulsions prepared presented a homogenous appearance, pH values compatible with the skin, a good stability, adequate rheological properties, and generally a pleasant sensation when were applied at cutaneous level, indicating the possibility of their use for skin care. 

Acknowledgment

      This paper was financially supported by “Carol Davila” University of Medicine and Pharmacy through Contract No. CNFIS-FDI-2020-0604 (MEDEX-III) funded by the Ministry of Education and Research, Romania, from the Institutional Development Fund for Public Universities – FDI 2020.

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