ALKALOIDS IN COSMETICS 233 caffeine, this alkaloid was applied at a concentration of 4.0 mg/mL ethanol/water (1:1, v/v) on the human skin membrane. The application volume was 25 μL/cm2, which was considered the minimum volume necessary to produce a homogeneous distribution on the skin surface. This represented a fi nite dose (100 μg/cm2), to mimic occupationally relevant situations. The exposure time was 24 h. Aliquots of the receptor fl uid were col- lected at various time points (minimally at 1, 2, 4, 8, and 24 h post-dosing). A cumula- tive amount absorbed per unit skin area versus time course was constructed from the amount of test substance in the receptor fl uid, and the maximum absorption rate was determined from the steepest, linear portion of the curve. The pene tration of caffeine through the skin depends on the ethnicity. Because of the greater number of sebaceous glands per square cm, caffeine is better absorbed by the skin of Asians in relation to the Caucasian. Mustafa et al. (14) studied the effect of different concentrations of caffeine (1, 3, and 5%) on in vitro release through synthetic membrane and on ex vivo permeation of this alkaloid through human skin. The lowest lag time (Tlag) and higher absorption rates were obtained with gel at 1% of caffeine applied at 1 mg/cm2. The diffusion fl ux of caffeine permeation does not depend on the concentration but rather on the quantity of formulation applied (15). In addit ion, there is a linear relationship between percutaneous caffeine penetration and transepidermal water loss (TEWL) (16). This was confi rmed in the studies by Lotte et al. (17). The authors of the presented studies applied to volunteers 20 μL radiolabelled 10-3 gCi/nmol caffeine to an area of 1 cm2. This alkaloid was applied on the forehead, postau- ricular area, arm (upper and outer), and abdomen. The highest TEWL values were ob- tained when caffeine was applied on the forehead (1.8), next when caffeine was applied on the postauricular area (1.2), on arm (1.0), and the lowest when caffeine was applied on the abdomen (0.9). The maximal absorption of caffeine is reached at 100 min after local ap- plication in vivo (18). Amnuaikit e t al. (19) performed experiment on the 34 volunteers divided into four groups, and the studies were taken for four successive days (about 8–9 volunteers/ group/d). They were assigned to lie on the bed but did not sleep for one night. No face washing in the next morning was allowed. The length of each puffy eye was immedi- ately measured using a thread starting from the corner of the eye near the nose to the end of the other side of the eye curving via the puffi ness and then the thread length was determined using a ruler. The swollen area under each eye was marked, and then the samples, i.e., a selected caffeine gel and its gel base, were randomly applied on different eyelids. The observations were taken at 10, 15, 30, 90, 150, and 180 min after apply- ing the gel formulations. Ahmadraji a nd Shatalebi ( 20) evaluated in vivo effi cacy of an anti-wrinkle and dark circle eye pad consisting of 3% caffeine and 1% vitamin K. Then, research was carried out on 11 healthy women. In a single blind trial, the sample pad was applied under the right eye, and the placebo pad, consisting of water, was placed under the left eye simultaneously. The content of water in the surface layer of the skin, the content of pigmentation, and the percent of elasticity of the skin were measured using apparatus multi-skin center MC 900. After 4 weeks, the skin around the right eye of all the subjects experienced a reduction in the depth of wrinkles and dark circles, and from a subjective point of view, the appearance and elasticity of the skin were improved. Topical caffeine use reduces blood fl ow by narrowing the blood vessels wherefore, this alkaloid reduces eye shadows and swelling, as well as signs of skin fatigue (21).
JOURNAL OF COSMETIC SCIENCE 234 Caffeine h as antioxidant properties, helping to fi ght free radicals, which play a role in accelerating the skin aging process. Combinations of caffeine and green tea polyphenols have been reported to have anti-wrinkle properties and the ability to brighten and fi rm up the skin in older individuals (22). The authors drew such conclusions on the basis of studies in which 126 women aged 30–70 years with mimic wrinkles (moderate to pro- nounced) took part. The women applied the selected product to half of their face twice a day (morning and evening) for 4 weeks. In the experiment, women from group 1 used daytime SPF 30 lotion, from group 2 used night cream, and from group 3 used eye cr eam containing caffeine. Authors did not present information on how much caffeine was in the topically applied product. The FOITS technique (Fast Optical In vivo Topometry o f human Skin) was used to measure changes in crow’s feet. In addition, changes in skin barrier function were determined using triplicate TEWL measurements. Four weeks of treatment with the caffeine preparation improved skin smoothness and reduced the depth of wrinkles (23). It has bee n reported that caffeine helps to stimulate hair growth and inhibit their loss (22). Benefi cial changes in the mechanical properties of individual scalp fi bers were ob- served after the caffeine preparation. Fisher et al. (24) took hair follicles from the vertex areas from 14 male patients. Hair follicles were cultivated for 120–192 h in vitro with normal William’s E medium (control) or William’s E medium containing different con- centrations of caffeine (0.001–0.15%). Hair shaft elongation was measured daily, and at the end of cultivation, cryosections of follicles were stained with Ki-67 to evaluate the degree and localization of keratinocyte proliferation. They showed that caffeine concen- trations ranging from 0.001% to 0.005% led to in vitro stimulation of human hair follicle growth. The stimulating effects of caffeine on hair growth can also be explained due to the caffeine phosphodiesterase inhibition activity with consequent increase of cAMP in- tracellular concentration and stimulating cellular metabolism (24). CAPSAICIN IN COSMETICS Capsaicin, (6E)-N-[( 4-hydroxy-3-methoxyphenyl) methyl]-8-methyl-6-nonenamide, is an active ingredient in capsicum plants (Figure 2). Capsaicin is obtained, among others, from fruits of chili peppers (Capsicum chili), jalapeño (Capsicum annuum ‘Jalapeño’), or cay- enne pepper (Capsicum annuum ‘Cayenne’) (25,26). It is known primarily for its character- istic sharp taste and irritating properties on nerve endings, which is used in the food, pharmaceutical, and cosmetics industries. Capsaicin has analgesic, antioxidant, weight loss, antibacterial, and thermoregulatory effects. Discussions are currently underway about the effect of capsaicin on cancer development. Test results of Hwang et al. (27) sug- gest that capsaicin may act as a cocarcinogen, and thus potentiate the carcinogenic effect of 2-O-tetradecanoyl phorbol-13-acetate (TPA). The properti es of capsaicin are used primarily in the pharmaceutical industry as an addi- tive to drugs that inhibit pain associated with rheumatoid arthritis and neuralgia. They have also been used in the cosmetic industry as active, fl avoring, or preservative agents (28). Applying a s mall amount of capsaicin to the skin causes a feeling of warmth or gentle burning. Because of the side effects of long doses of capsaicin, such as secondary hyperal- gesia, the maximum use of capsaicin treatment in drugs is 0.075%. On the other hand,
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