The importance of the vehicle in

Transcription

1 J. Soc. Cosmet. Chem (1972) 1972 Society of Cosmetic Chemists of Great Britain The importance of the vehicle in formulating sunscreen and tanning preparations E. R. KRAFT,* S. G. HOCH*, R. A. QUISNO* AND E. A. NEWCOMB* Presented on 6th October 1970 in London at the Symposium on 'New developments in lanolin and its derivatives', organized by the Society of Cosmetic Chemists and the Society of Cosmetic Chemists of Great Britain. Synopsis--This study was undertaken to determine the functional significance of the VEHICLE in SUNTAN PREPARATIONS. Three o/w vehicles, three oil-based vehicles and two controls were tested on HUMAN subjects under both natural SUNLIGHT and ARTIFICIAL LIGHT (a xenon-mercury lamp developed by one of the authors). The same screening agent was used in each vehicle. In general, the oil-based vehicles gave superior protection against sunburn. The o/w EMULSIONS were superior in promoting tanning although one oil-based vehicle gave good results in protection against burn and in promoting tanning. Previous work in the field of sunscreen studies has placed a great deal of emphasis on the importance of the sunscreen used, and correlations have been made between the efficacy of a sunscreen and the protection given by a finished product (1). In addition to the active sunscreen ingredient, the vehicle may play a far more important role than formerly thought. We believe the following factors should be considered: (1) The concentration of sunscreen in the original product versus concentration on the skin after water evaporation. (2) The emulsion remaining on the skin after water evaporation, and the washability and the susceptibility to re-emulsification when exposed to perspiration and bathing. * Maimstrom Chemical Corporation, Linden, N.J , U.S.A.? Hill Top Research Inc, Miamiville, Ohio, U.S.A. 383

2 384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (3) The function of a vehicle in increasing product penetration and/or substantivity to the skin. (4) The function of a sunscreen vehicle to augment and replace skin lipids, essential in returning erythematous skin to normal. The vehicle thus may not only influence the total concentration of sunscreen on the skin surface, but also its skin penetration, substantivity to skin, washability, and the rate and extent to which the treated skin is damaged and returns to normal. Early pilot studies (2) compared the sunscreen effect of oil-based products containing sunscreens, and o/w emulsions containing no screening agents versus untreated skin. These studies indicated that some sun protection was given by the o/w emulsions. The most dramatic effects were in promoting normal skin recovery with less peeling. It may be significanto note that two effective emulsions contained a known moisturizing lipid. However, the inclusion of this lipid in the oil-based products did not seem to give the same result. This study indicated the importance of using a lipid moisturizer in conjunction with water in sunscreen and after-sun treatment products. A private report by Klauder (3) also emphasized post-treatment improvement using two o/w emulsions. A uniformly greater improvement was shown with the product containing a lipid moisturizing agent (4). Moisturizing is not the complete answer to the problem of treating dry and sunburnt skin. Skin undergoing erythematous changes has a demand for oil as well as water. Skin lipids play a major role in maintaining a normal condition in the stratum corneum, (1) as a partially occlusive barrier to excessive moisture loss, (2) as binding agents to hold the cornified epithelial cells in place, and (3) as lubricants for the laminae to give a feeling of softness and pliability to the whole stratum corneum (5). In order to further evaluate vehicle importance in sunscreen preparations, a clinical study was initiated (8), six vehicles being used with the same sunscreen. The sunscreen was Dipsal (di-propylene glycol salicylate) and it was used at 35/0 concentration in all six formulations. Three formulations were o/w emulsions: GS/1, G8/2 and G8/3 (Table I). One of these formulations contained 55/0 Lantrol (the liquid de-waxed fraction of lanolin), another a control with 55/0 isopropyl myristate replacing the Lantrol % and a third containing 55/0 of an iodine Lantrol complex. The other three were oil-based formulations derived from the formula- tions in Military Specification 11262C. The first, G8/4, contained Lantrol,

3 SUNSCREEN AND TANNING PREPARATIONS 385 the second, G8/5, replaced this derivative with 2 o sesame oil and 3 o of 70 viscosity mineral oil, and the third, G8/6, replaced the Lantrol with the iodine Lantrol complex. Controls were G8/7--Lantrol and G8/8-- iodine Lantrol Table I O/w formulations G8/1 G8/2 G8/3 Phase I Iodized Lantrol m 5.00 Stearic acid isopropyl myristate œantrol Silicone fluid Dehydroacetic acid Dipsal Halby dilauryl thiodipropionate Phase II Water Glycerine Propylene glycol % Carbopo1934 solution Sequestrene N Tegosept M Phase III Water Potassium hydroxide Perfume Total Table II Oil-based formulations G8/4 G8/5 GS/6 Dipsal Light amber petrol Stearyl alcohol Mineral oil of viscosity Lantrol 5.0 Calcium stearate Kaolin Perfume Sesame oil Iodized Lantrol Total

4 386 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS All K values were run on a standard Beckmann D U spectrophotometer. The o/w emulsions were run according to standard methods (6) and all had similar Kvalues at max. (absorption wave length). For the oil-based formulations, the method outlined in the military specifications was extremely difficult to use, since it stipulated a film thickness of mm. Commercial cells of this light path length are designed for liquids, not for creams or semi-solids. Since the formulations contained kaolin it was difficult to lay down a thin film and obtain an accurate reading. We discussed this problem with the Military Laboratory in Natick, Mass., which set up this procedure. It was stated that the present method had many drawbacks, especially the fact that at certain temperatures the product becomes opaque on cooling and gives an absorbance reading even with no sunscreen present. The military transmittance specification is in the process of being revised by the U.S. Army Natick Laboratory. It therefore seemed appropriate to take up the formulation G8/5 (containing sesame oil and mineral oil) in isopropanol in the standard manner. The kaolin was allowed to settle and the reading was taken on the remainder of the solution. The K value was the same as the o/w emulsions. Human studies on these formulations were run in both natural sunlight and artificial light. Harry (7) quotes Stambovsky to point out the deficiency of sunscreen testing with artificial light, since it is lacking in ir energy which increasesensitivity of the skin to uv radiation. Since the age-old conflict of artificial light versus sunlight in sunscreen evaluations has not been resolved, it was decided to utilize sunlight in the following study and then compare the results with an artificial light source study (9). ] ATURAL SUNLIGHT STUDY Procedure The six formulations and two controls mentioned earlier were tested in a Florida sunlight study. Eleven adult female subjects were enrolled in this study. These subjects had not been previously exposed to the sun and the skin of each was free from erythema and tanning. The temperature was approx. 26.6øC and the sun shone approx. 95 o of the time. When the sun was not out, there was a bright hazy condition still conducive to sun burning. The wind varied from 3.1 to 6.2 km h -x. Reflected light readings were taken using a Weston Master Hlight meter.

5 SUNSCREEN AND TANNING PREPARATIONS 387 This was done in order to give some base of light intensity for future reference. Readings varied from 150 Weston light units (5 o of the time) to 400 (95 o of the time) when the meter was 150 mm from the subject. The test materials, in amounts of approximately g, were applied to eight test areas, each about 5.08 cm 2, using a 2 ml syringe. The MED (minimal erythematogenic dose) and control sites were areas of 2.54 cm 2. The material was rubbed into the skin with a tongue depressor and the positions of the samples on the back were randomized. Exposure sites were delineated by the use of Duke* elastic tape. The subject's back was covered with terry cloth excepthe areas to be exposed. At 10 min intervals for 40 min, a 2.54 cm section was progressively covered in order to determine the MED. The MED was calculated for each subject on the following day. The treatment sites were exposed for approximately 3 h. This was equivalent to x MED. All sites were read in natural daylight and were scored on days 1, 3, 4, 5, 6, 7, 8 and 10 according to the scale in Table III. Table III Scoring scale--sunlight 0 No erythema 1 Barely perceptible erythema 2 Moderate erythema 3 Severe erythema 4 Blistering 5 Peeling 00 No tanning 01 Slight tanning 02 Marked tanning RA Raw area S H Scab Healing Results The role of sunscreen and vehicl efficacy falls into two classes--sunburn protection and ability to promote tanning. As shown in Table IV, samples were ranked for sunburn protection, using a base of 176 as little or no protection. Samples were ranked for promotion of tanning using a score of 8 as a control base. For the final ranking, composite scores of all subjects on days 1, 3, 6, 10, and on the final day were used. The data for sunburn protection and tanning efficacy is summarized in Table IV. *Tape MFG (Duke Laboratories South Norwalk, Connecticut, U.S.A.).

6 388 JOURNAL OF THE SOCIETY OF COSMETI CHEMISTS Table IV Sunlight Sunburn Tanning Total % Total % Sample score protection score stimulation GS/ G8/ G8/ G8/ G8/ G8/ G8/ G8/ Untreated control Conclusions For sunburn protection it is evidenthat the best sun protection is gained through the oil-based formulations. The same percentage of sunscreen agent is present in all formulations, G8/1-6. It may be speculated that the evaporation of water from the emulsion formulations, though leaving a more concentrated sunscreen film on the skin, affords less sun protection. This may be attributed to a thinner sunscreen film, since 20 parts oil phase and sunscreen remain after the evaporation of water from the o/w formulation, against no evaporation from 100 parts oil-base formulation. Thus, volume of film remaining is one-fifth as much, yet sunscreen concentration is five times as much in the less effective formula. The greater residual volume of film probably results in a more continuous coverage by the oil-base formula. After studying the tanning effect, the most efficientanning agents were the preparations which were emulsions. These formulations increased the skin tanning potential. Their use resulted in less blistering, less peeling and improved tanning. The one exception was formulation G8/4, which compared favourably with the o/w emulsions in the promotion of tanning. G8/4 contains Lantrol lanolin oil, at the concentration of 5%. It is our contention, as speculated in the early portion of this paper, that Lantrol has improved the moisture retention properties of the skin. Since it is essential to return the moisture balance of the skin to normal to assure good healing, we have an oil-base formulation which accomplishes this by virtue of Lantrol. Thus, one achieves the sun protection of an oil-base product along with the tanning and skin healing effects of an emulsion.

7 SUNSCREEN AND TANNING PREPARATIONS 389 ARTIFICIAL LIGHT STUDY Procedure The same formulations and controls were utilized in the artificial light procedure as in the sunlight study. Exposure to uv irradiation was from a xenon mercury lamp (XeM, developed by Hill Top Research, Inc.) (9). The bulbs in this lamp are rated at 700 W, and the lamp is equipped with a filter which excludes all radiation below 260 nm and passes very little between 260 and 270 nm. The output of this lamp, between 280 and 320 nm is about 6.5 of the total energy. The output of a pure xenon lamp in this area is about 1.5 o. The ir (heat) output of this lamp is only about 5.2 o of the total energy, while that of a pure xenon is about 38.5 o. The output W cm -2 in the range of nm is adjustable by means of voltage control from to I This can be increased to by employing a second individually controlled lamp which is present in the unit. With settings providing W cm - ' the MED on untanned skin is between 7 and 1/5 s on most subjects. By means of a template, an exposure area of I 17 x 43 mm was marked off on the lateral aspects of both thighs of the test subjects. These rectangular areas were subdivided into five equal areas of about 23 x 43 mm. One of the eight test materials was applied to a strip 15 x 43 mm on each of these areas. The order of application was randomized on each subject. Approximately 0.05 ml of the test material was applied from a I ml syringe, and spread thinly over this area by means of a 15 mm wooden tongue depressor. One oœ the l0 marked areas did not receive any treatment and one area was covered with a piece of opaque paper masking tape. The lamp was positioned so that the exposure area would coincide with the marked treatment area. The light shutter was opened and each thigh was exposed to the light source for 60 s. The erythema present in each treated and exposed area was scored after 24, 48 and 72 h. The scoring scale used is shown in Table V. Table V Scoring scale--artificial light 0 No erytherna 0.5 Barely perceptible erythema 1 Slight erytherna 2 Moderate erythema 3 Marked erythema

8 390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Results The results were treated in a fashion similar to those for the Florida sun- light study. They were ranked for protection from sunburn only. A score of 40.0 (Table VI) indicated no protection from burning. Table VI Artificial light Sample Total score 5/o of control 5/o protection G8/ G8/ G8/ O 80 G8/ G8/ G8/ G8/ G8/ Control Summary The results of this study (9) agreed in general with the results presented in the Florida sunlight study (8). From the artificial light study, it was difficult to judge tanning efficacy and the tanning results could not be considered conclusive; hence the data are not reported. Later studies indicated that changes in technique lead to better evaluation of tanning. The artificial light (XeM) technique should be reserved for screening of new experimental products. It is not intended to be a substitute for natural sunlight in final evaluations. CONCLUSIONS The emulsion vehicles afforded significantly less protection against burn than did the oil-based formulas. G8/4, Lantrol oil-based formulation, gave similar protection when compared to the other two oil-based types. In general the better sunscreen products did not give the best tanning results. However, oil-based formulation, G8/4 with Lantrol, not only gave between 86 and 92 o sunscreen protection, but was also effective in promoting tanning. (Received: 18th October 1971)

9 SUNSCREEN AND TANNING PREPARATIONS 391 REFERENCES (1) Willis, I. and Kligman, A.M. The evaluation of sunscreens by human assay. J. Soc. Cosmet. Chern (1969). (2) Private report No. M-9139, Rosner-Hixson Laboratories (August 1959). (3) Private report, Treatment of sunburn, J. V. Klauder (June 1959). (4) The moisturizing plus story (Maimstrom Chemical Corp., Linden, N.J.). (5) Frazer, C. N. and Blank, H. I. A formulary for external therapy of the skin, 55 (1954) (Bannerstone House, Springfield, Ill.). (6) Kreps, S. I. Spectrophotometric evaluation of sun screens. Proc. Sci. Sect. Toilet Goods Ass (May 1955). (7) Harry, R. G. Cosrnetics--Theirprinciples andpractices, 257 (1956) (Chemical Publishing Co., New York). (8) Private report HTS-5, Sun screen efficacy study (December 30, 1968) (Hill Top Research, Inc.). (9) Private report T-132, Evaluation of sun screen properties (artificial light) (May 1969) (Hill Top Research Inc.).