1. United States Food and Drug Administration (FDA) (2013) FDA authority over cosmetics: how cosmetics are not FDA-approved, but are FDA-regulated,” U.S. Food and Drug Administration. [Online]
https://www.fda.gov/cosmetics/cosmetics-laws-regulations/fda-authority-over-cosmetics-how-cosmetics-are-not-fda-approved-are-fda-regulated
. Accessed 1 Oct 2020
2. Yourick J, Bronaugh R (2005) Percutaneous absorption of hair dyes. In: Bronaugh RL, Maibach HI (eds) Percutaneous absorption: drugs, cosmetics, mechanisms, methodology. Taylor & Francis, Boca Raton, FL, pp 641–658
3. Wolfram L, Maibach H (2005) Hair dye penetration in monkey and man. In: Bronaugh RL, Maibach HI (eds) Percutaneous absorption:drugs, cosmetics, mechanisms, methodology. Taylor & Francis, Boca Raton, FL, pp 659–670
4. Frenkel EP, Brody F (1973) Percutaneous absorption and elimination of an aromatic hair dye. Arch Environ Health 27(6):401–404
5. Howes D, Black JG (1983) Percutaneous absorption of 2-nitro-p-phenylenediamine. Int J Cosmet Sci 5(5):215–226