Development of a Methodology for Assessing Primary Dermal Irritation, Cumulative Irritation, and Skin Sensitization of Nail Products
Author: Silva, Rafaella L.; Carli, Barbrara F.; Florencio, Cristiane P.; Guimarães, Anna C.M.; Silva, Jéssica S.S.; Asbahr, Márcia R.M.S.; Eberlin, Samara1, Pinheiro, Ana L. T. A.1; Pinheiro, Adriano S.1
Published at: September 15, 2025
The safety of nail polishes is a significant concern due to the frequent exposure of nails and skin to their components, including solvents, resins, pigments, plasticizers, and thixotropic agents. These ingredients play essential roles, such as providing durability and flexibility to the product, but may contain chemical substances like formaldehyde, toluene, and mica, which are associated with sensitization, contact dermatitis, allergic reactions, and skin irritation. These factors underscore the importance of rigorous and meticulous control in the formulation of such products to ensure consumer safety. Primary and cumulative dermal irritability, as well as sensitization, providing scientific support for claims such as dermatologically tested, non-irritating, and non-sensitizing. Primary dermal irritability was evaluated on the fingernails of the right hand's little and ring fingers, with assessments conducted at 48 and 96 hours. For cumulative irritability, the product was applied to the fingernails of the right hand's middle and index fingers, using the left hand as a control, across nine applications over three weeks. Following a ten-day rest period, the challenge phase began, during which the product was applied to the right thumb (virgin area) while the left thumb served as a control. All reactions were classified according to the ICDRG (International Contact Dermatitis Research Group) criteria and a specific scoring system for nail alterations, with predefined evaluation time points. The pilot study, conducted with 65 participants, evaluated a nail polish containing organic solvents, nitrocellulose, resins, pigments, and plasticizers. The Individual Dermal Irritation Index (IdiI) was calculated for each participant, and the Mean Dermal Irritation Index (MdiI) was used to classify the product. Classification criteria included: MdiI=0.0 (non-irritating - excellent compatibility), MdiI<0.2 (non-irritating - good compatibility), with higher ranges indicating varying degrees of irritation. The product showed an IdiI of 0.00 and was classified as non-irritating with excellent dermal compatibility. The methodology proved effective in identifying adverse reactions, confirming the product as non-irritating and non-sensitizing. These findings support the safety and regulatory compliance of nail products and promote the development of dermatologically safe cosmetics for nail use.