A Novel Multifactorial Approach to Developing Mild Laundry Detergents and Assessing Their Relative Mildness

informed recommendations on laundry detergent choices for their patients with sensitive skin.³

The objective of this work was to create an especially mild laundry detergent formulation through development in partnership with dermatologists (DPD formulation) and concurrent comparison of its mildness profile with existing mild laundry detergents. During formulation development, the ingredients were carefully selected and the surfactant composition was optimized. The potential mildness of the nal formulation was further supported by utilizing unique scientific tests including the zein solubility assay, corneosurfametry (CSM), and Cytokine Assay of Il-1α production. These tests evaluate protein denaturation, overall stratum corneal damage, and keratinocyte-derived IL-1α response, respectively. The Detergent Mildness Index (DMI) was developed, which establishes a composite score to rank the irritancy potential of laundry detergents that are marketed for patients with sensitive skin.

Twelve detergents, including the new DPD formulation, were tested. They comprise 85% market share of the existing Sen- sitive Skin laundry detergent category. The total surfactant percentage in the category ranges from 10% – 28%.

The zein solubility assay is an in vitro method. Zein protein is structurally similar to keratin. Both are insoluble in aqueous solution unless they are denatured. Irritancy is determined by measuring the amount of solubilized zein after detergent exposure.³ In this study, zein powder was mixed with detergent solutions for about one hour. Blank surfactant solutions were prepared in the same manner. Undissolved zein were removed by ltration and the ltrate dried.The total percentage of solubilized zein was calculated by measuring the amount of zein solubilized by the detergent solution.The percentage of solubilized zein corresponds to the degree of surfactant-induced protein denaturation.¹³

Corneosurfametry (CSM) is an ex vivo method, which measures the level of interaction between the SC and detergent.⁴ Superficial layers of the SC are collected from healthy volunteers using tapes that are then placed in detergent solution. They are then stained using a dye solution to assess the degree of SC damage. A high degree of staining re ects a highly irritating detergent.³ In this study, samples were collected using Book tape strips. Volunteers were recruited by passing a pre-screening survey for inclusion and exclusion guidelines. Tapes were placed on volunteer’s forearms and gently rubbed onto skin before removal. Tapes were then immersed in detergent solutions, dried, and then placed in Basic Fuschin Blue Dye. Once dry, samples are placed on transparency lms and analyzed using a spectrophotometer. The colorimetric index of mildness (CIM) was calculated using the following formula: CIM = (L* - C*), where L* corresponds to mean luminancy and C* to Chroma.¹⁴ This calculation measures the degree of dye saturation, and consequently, the level of damage to SC proteins and lipids.12

In this study, the EpiDermTM Skin Model (MakTek Corporation) assessed potential dermal irritation secondary to detergent exposure. Samples were analyzed using an MTT (3-[4,5-dimeth- ylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) conversion assay after exposure to detergent solutions in sterile, deionized water. Each sample was added to 1.0 mg/mL MTT (Sigma) solution in warm Dulbecco’s Modified Eagle’s Medium (DMEM) containing 2 mM L-glutamine (MTT Addition Medium) to assess its ability to directly reduce MTT. This measures the NAD(P)H- dependent microsomal enzyme reduction of MTT (and to a lesser extent, the succinate dehydrogenase reduction of MTT) to a blue formazan precipitate. Samples were incubated for 24 hours, and gently agitated to evenly mix cytokine released into the medium. Samples were added to microtiter plates which were previously coated with IL-1α detection antibodies. After incubation for 2 hours at room temperature, samples were rinsed with wash solution. Enzyme conjugate (IL-1α Conjugate) secondary antibody was added to the samples and incubated for another 20 minutes. Stop solution was added to halt the reaction. Finally, samples were read at 450nm using a Molecular Devices’ Vmax plate reader within 30 minutes of stopping the reaction to measure the amount of IL-1α released in response to each detergent.¹³

The new DPD formulation was ranked mildest across each measure tested in this study: zein, CSM, cytokine, and DMI.

As shown in Figure 1, a smaller percentage of zein was solubilized when placed in the new DPD formulation, compared to other mild detergents. The harshest detergent, Product 11 solubilized more than twice the amount of zein solubilized by DPD formula. The difference between DPD formula and other samples were found to be statistically significant, with the exception of Product 3. The similarity of zein protein to keratin allows us to