196 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS INTRODUCTION It has long been recognized that cyclic hair growth activity occurs in a random mosaic pattern in which each hair enters anagen (active growing phase), catagen (involutional phase), and telogen (resting phase) independent of other hairs. This results in a daily shedding process in which telogen hairs are shedded and replaced by new anagen hairs (2-7,9-10). Since 85% to 90% of the hair is in the anagen phase and there are approximately 100,000 hairs on the head, the reported average daily telogen hair loss ranges anywhere from 34.8 hairs (2), 40-100 hairs (3), 100 hairs (4,7), 100-150 hairs (5), to 100-180 hairs (6). In general, the anagen phase is longer in women than in men (5). During pregnancy, the proportion of hairs in anagen phase may increase to greater than 95%, thereby decreasing the average shedding rate to 15-20 hairs per day (5). Many factors can lead to increased, abnormal hair loss (4,7,9-22). These include hor- monal changes (3,7,9-22), acute and chronic illness (4,7,9-14), scalp infections (3,7,9-14), trauma (3,7,9-15), medication (3,7,9-22), nutritional deficiency (9-22), endocrine disorders (3,7,9-14), and hereditary predilection (3,7,9-14). Although in- correctly used perms and hair colorants can lead to hair breakage as a result of overpro- cessing during chemical modification (1), shampoos have long been recognized as safe for use on hair (1). Most traditional shampoos contain anionic surfactants to cleanse the hair. Conditioners contain fatty alcohols and cationic surfactants to lubricate and neutralize the negative charges on the hair. Since anionic surfactants are negatively charged and cationic sur- factants are positively charged, the cleansing and conditioning functions from tradi- tional shampoos and conditioners have to be separated in a two-step process because they cannot exist together in one product. Dimethicone shampoos differ from traditional shampoos in that they clean and condition hair in a single step. This is achieved by the deposition of non-charged hydrophobic dimethicone droplets to condition hair without interfering with the cleaning ability of the anionic surfactants (23). MATERIALS AND METHODS GENERAL OUTLINE A total of 460 Thai females between the ages of 18 and 60 years were screened for eligibility to participate in the study. Prior to participation, they were questioned by dermatologists regarding their medical history and medication intake. The subjects then underwent scalp and hair examinations to assess the severity of scalp flaking and in- flammation, the presence or absence of scalp diseases, the degree of hair dryness and hair damage, and abnormal hair loss. The severity of scalp flaking was assessed on a 5-point scale ranging from no flaking (0) to severe flaking (5). Scalp erythema, if present, was assessed on a 4-point scale ranging from slight (1) to severe (4). Scalp disease was assessed on a 5-point scale where 1 represented non-diseased scalp, 2 represented dandruff, 3 represented seborrheic der- matitis, 4 represented psoriasis, and 5 represented eczema. Hair dryness was assessed on

ABSENCE OF EFFECTS OF DIMETHICONE ON HAIR LOSS 197 a 4-point scale where 1 represented oily hair and 4 represented dry hair. Hair damage was assessed in a similar manner on a 4-point scale where 1 represented undamaged hair and 4 represented severely damaged hair. The hair dryness and hair damage scores were totalled and used as a stratification criterion for the balance and assignment of subjects in the study. Subjects were assessed for abnormal hair loss using the following criteria: the pull test (3), the evaluation of short hairs at the hair part for tapered and blunt hair characteristics, and the assessment of the width of the hair part for hair thinning. Other means of assessing abnormal hair loss, such as the pluck test (3) were considered, but the pluck test was not implemented since this procedure entailed significant pain and some hair loss from plucking in a group of healthy normals not in a hair growth study. Subjects deemed healthy, not on chronic medication with the exception of oral contra- ceptives, not having scalp diseases (including psoriasis, seborrheic dermatitis, and ec- zema), and not having scalp inflammation or any abnormal hair loss, were enrolled in the study. A total of 440 females were enrolled. Prior to participation, these subjects were carefully instructed how to collect all shed hair. Special drains were installed in the bathrooms and sinks of each home to aid the complete collection of shed hair. Subjects were requested to maintain their normal routine hair care regimen for two weeks. During this period, they were supervised by field workers on how to collect all shed hair from the sinks, drains, towels, combs, brushes, and pillows on a daily basis. Premarked envelopes were distributed to the subjects to retain the daily collected hair. Field workers visited each subject's home every two to three days to collect the envelopes of hair, redistribute new envelopes for the next set of collections, supervise the hair collection, distribute products, and answer any questions the subject may have had on hair collection and the study. After the two-week baseline period, subjects were assigned to the following shampoo treatments, using random permutations of three after being stratified on total hair dryness and damage scores of 0 to 6 and 7 to 8, and as to whether they used shampoo products only, used shampoo and conditioner products, or used a 2-in-1 dimethicone- containing shampoo as their normal hair care regimen. Number of Group Treatment subjects I Dimethicone-containing 2-in-1 shampoo 145 II Non-dimethicone-containing shampoo 145 III Dimethicone-containing shampoo 145 This was a double-blind study. To ensure blindness, the three shampoo products were packaged in identical containers without identification and were distributed by field personnel from Deemar Survey Research Group. The evaluation team from the Thai Institute of Dermatology had no knowledge of what each subject used. Subjects used the assigned test product ad libitum, at least three times a week for a period of four weeks. The frequency of test product use was recorded on both the envelopes of daily hair collection and the product use diaries. Product consumption was determined pre- and posttreatment. During the treatment phase, the subjects collected all shed hair from the sinks, drains, towels, combs, brushes, and pillows for a period of four weeks.