Triethanolamine is an amine produced by reacting ethylene oxide (considered highly toxic) with ammonia (another known toxin). Used in in a variety of cosmetic and personal care products, including eyeliners, mascara, eye shadows, blushers, make-up bases and foundations, as well as in fragrances, hair care products, hair dyes, wave sets, shaving products, sunscreens, and skin care and skin cleansing products as a pH balancer and emulsion stabilizer. Like all amines, it has the potential for creating nitrosamines. There's a controversy as to whether or not this poses a real problem for skin, given the low concentrations used in cosmetics and the theory that nitrosamines cannot penetrate skin.
Triethanaolime is typically used in amounts less than 1% in cosmetics; concentrations of 2.5% have been found to be non-irritating when applied to skin. It is also added to foods.
According to OrganicConsumers.org, Triethanolamine can cause allergic reactions including eye problems, dryness of hair and skin, and could be toxic if absorbed into the body over a long period of time. It can cause itching, burning, scaling, hives, and blistering of skin, all symptoms which may increase with higher concentrations (The Green Beauty Guide).
Reference for this information:
International Journal of Toxicology, May-June 2013, pages 59S-83S
Contact Dermatitis, May 2009, pages 243-255
Regulatory Toxicology and Pharmacology, October 2005, pages 10-18