The formulation and evaluation of urea containing products
Claasen, Cornelia Isabella
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Almost every person will experience dry skin during his or her lifetime. Many people experience occasional episodes, but some have a chronic problem with xerosis that is irritating and troublesome. Moisturisers are the mainstay of treatment for dry skin, daily maintenance of normal skin, and adjunctive therapy for many skin diseases (Flynn et al., 2001:387). The objectives of this study were the formulation and evaluation of urea containing products. Seven different cosmetic products were formulated: hair gel, shampoo, facial toner, facial cleanser, day cream, foot and heel balm and a body cream. The product development program started with a pre-formulation study, followed by formulation of the seven skin care products, which were followed by stability testing, based on the requirements of the South African Medicines Control Council (2003:21, 22, 23) for new products. The stability of all skin care products must he matched to the expected period of usage by the consumer, as well as to the user's requirements. The formulations were tested under ICH conditions (accelerated stability studies) over a period of three months at three different storage temperatures, i.e. 5°C, 25°C/60%/RH, 40°C/75%RH. Stability indicating tests that applied to these formulations, were conducted: pH, relative density, viscosity, appearance, penetration, spreadability, assay of urea, the assays of the preservatives and the release study of urea by means of membrane release. Chapter 1 gives a literature overview of the skin and the properties and uses of urea. Chapter 2 deals with the formulation of the urea products and the chemicals that have been used. Chapter 3 describes the methods used for accelerated stability testing. Chapter 4 finally deals with the results obtained and the conclusions that were made. The test results showed the following: There was a prominent change in the pH of all the formulated products, this can be due to the decomposition of urea into carbon dioxide and ammonia (Beiersdorf, 2003). Higher temperature and moisture increase this decomposition and cause the pH to increase to values as high as 9 (Anon, 2003:20). However, urea compositions can be stabilised when they contain methylsulfonylmethane (MSM) (Herschler, 1981:l). The viscosity, spreadability, penetration, relative density and appearance of the products remained more or less the same over three months, except for the day cream and the facial cleanser where phase separation occurred after 1 month. The urea content decreased with time, but only dropped to below 90% in the day cream after 3 months at 4O°C/75% RH. HPLC analysis of the preservatives confirmed their stability in the formulated products. The preservative efficacy results proved that the products were sufficiently protected from microbial contamination. The release study indicated that urea is released at a steady rate from the preparations tested. The release of urea from the hair gel is about four times faster than that from the body cream and the foot and heel balm. In general, the release is influenced by the viscosity of the medium and should be faster from the gel than from the creams (Shah et al., 1991:55). In conclusion it can be said that urea was successfully formulated into the seven cosmetic products except for the facial cleanser and day cream which must be stabilised.
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