It's a little helper ingredient that helps to set the pH of the products to be right. It has an alkaline pH and can neutralize acidic ingredients.

https://incidecoder.com/ingredients/tromethamine

【Tromethamine】

Rating: AVERAGE
Categories: pH Adjuster/Stabilizer

Tromethamine is a triol, a type of alcohol that contains three hydroxyl groups which consist of bonded hydrogen and oxygen atoms. It serves as a pH adjusting ingredient in skin care formulations.

When used in cosmetic formulas it assists in neutralizing more acidic substances due to its alkaline pH. Although skin is naturally acidic, with a pH ranging between 4 and 5, altering skin’s natural delicate pH balance can cause irritation. The balance that tromethamine brings to a formula’s pH can help prevent this.

As a raw material tromethamine appears as a white crystalline powder. The Cosmetic Ingredient Review Expert Panel concluded that it’s safe for use in current cosmetic preparations. It’s commonly used in concentrations between 0.00009–3.7%.

Outside of cosmetics, tromethamine is used in medical applications to reduce acidity.

https://www.paulaschoice.com/ingredient-dictionary/ingredient-tromethamine.html