Modern disposable diapers are complex products and ubiquitous globally. A robust safety assessment for disposable diapers include two important exposure parameters, i) frequency of diaper use & ii) constituent transfer from diaper to skin from direct and indirect skin contact materials. This article uses published information and original studies to quantify the exposure parameters for diapers. Using growth tables for the first three years of diapered life, an average body weight of 10-11 kg can be calculated, with a 10th percentile for females (8.5-8.8 kg). Data from surveys and diary studies were conducted to determine the frequency of use of diapers. The overall mean in the US is 4.7 diapers per day with a 75th, 90th, and 95th percentile of 5.0, 6.0, and 7.0 respectively. Using diaper topsheet-lotion transfer as a model, direct transfer to skin from the topsheet was 3.0-4.3% of the starting amount of lotion. Indirect transfer of diaper core materials as a measure of re-wetting of the skin via urine resurfacing back to the topsheet under pressure was estimated at a range of 0.32-0.66% averaging 0.46%. As described, a thorough data-based understanding of exposure is critical for a robust exposure based safety assessment of disposable diapers.

The dose-response relationship among dietary fiber, colonic fermentation, fecal weight, and mucosal growth were evaluated in this study. The morphometric parameter of total mucosal volume was used to assess diet-induced differences in colonic mucosal growth. Dietary fibers with a wide range of fermentability and that have previously been shown to inhibit the development of colonic neoplasia in rats were used. Sprague-Dawley rats were fed Purina Rodent Chow, AIN-76a fiber-free diet, or an AIN-76a diet supplemented with three different dietary fibers, (cellulose, guar gum, or wheat bran) at 2, 5, 10, or 15% of the diet. Diets were fed for 28 days. Total colonic mucosal volume was determined using stereologic principles and computerized image analysis; 48-hr fecal weight was measured; and the concentration of short-chain fatty acids (SCFA) in colonic contents was determined at study termination. Each type of fiber induced a dose-dependent increase in total mucosal volume of the colon and fecal weight. Mucosal volume and fecal weight were closely correlated (R2 > 0.95). Total mucosal volume was not correlated with the concentration of total SCFA or butyrate in the colon. These results indicate that diet-induced change in colonic mucosal growth, as measured by total mucosal volume, is positively correlated with fecal weight and not related to alterations in colonic fermentation. Enhanced colonic mucosal growth occurs in rats fed dietary fibers that have previously been shown to inhibit the development of genotoxin-induced colonic neoplasia in rats.

The colonic mucosa can adapt its growth to alterations in diet. Metabolites from colonic microflora are frequently implicated as the primary factor in mediating the colonic mucosal response to diet; however, there is also evidence indicating that diet may have a direct effect in mediating this response. The aim of this study was to determine the role of diet, microflora, and microflora metabolites in altering the growth of the colonic mucosa. Two 28-day feeding studies were conducted using Sprague-Dawley rats. The first study compared the growth of the colonic mucosa in germ-free and conventional rats fed 6 different diets. The second study compared the growth of the colonic mucosa to the concentration of bacterial-derived short-chain fatty acids (SCFAs), bile acids, and ammonia. The diets that were fed consisted of (1) AIN-76a diet without dietary fiber; (2) standard AIN-76a diet, which contained 5% cellulose; (3) AIN-76a diet with 5% guar gum; (4) a "Western" human diet with 20% fat and 10% cellulose; (5) AIN-76a diet formulated to mimic Diet 4 in fat content but with 2.5% cellulose; and (6) Purina Rodent Chow. Quantitative volumetric and stereologic analysis was used to assess changes in total colonic mucosal volume as a measure of mucosal growth. In germ-free rats, Diets 2-4 and 6 induced a significant increase (18-38%) in mucosal volume compared to Diet 1. In conventional animals, only Diets 4 and 6 induced a significant increase (up to 63%) in mucosal volume compared to Diet 1. Relative to the germ-free animals, only conventional animals on Diets 4 and 6 had an increase in mucosal volume. The increases in mucosal volume in Diets 4 and 6 were not consistently associated with increased SCFAs, ammonia, or bile acids. There was a wide range in the colonic concentrations of SCFAs (2-fold), ammonia (6-fold), and bile acids (10-fold). The presence of colonic microflora in and of itself does not lead to enhanced colonic mucosal growth. Rather, there are unique interactions between specific types of diet and microflora that lead to a growth-promoting effect. This effect could not be explained by alterations in the concentration of SCFAs, ammonia, or bile acids in colonic contents.

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