The ingredients most commonly responsible for allergic reactions were waxes, castor oil, colophony, gallate, and benzophenone-3.

Waxes of various types were identified as causative agents in 8 cases of contact dermatitis that followed the use of lip care products. Propolis (produced by bees) was identified in 4 cases, and ceresin and candelilla wax were identified in 2 cases each. The remaining cases were attributed to carnauba wax alone or in combination with propolis (1 case each).
A total of 7 studies reported reactions to castor oil or components such as ricinoleic acid (including synthetic ricinoleate). Some research suggests that dermatitis can occur as a result of cross-reaction between ricinoleic acid and other ingredients such as oleyl alcohol, lanolin, and castor oil.^[1]
Colophony, also known as rosin, is a substance obtained from coniferous trees. This review identified 6 cases of allergic contact dermatitis in response to rosin or its derivatives (ester gum and pentaerythritol rosinate).
A total of 5 cases were attributed to gallate, which is an ester of gallic acid. The most common formulation is propyl gallate, which was identified in 4 cases. The remaining case was attributed to both octyl gallate and dodecyl gallate.
A total of 5 cases of allergic reactions attributed to benzophenone-3. Benzophenone-3, also known as oxybenzone, is a UV-absorbing agent commonly used in sunscreen. It is also used as a photostabilizer in lip care and cosmetic products. Benzophenone-3 is a small molecule, capable of absorption through skin, and has been proposed as the main allergen in cases of sunscreen reactions.^[2]

The authors also noted a case series in which 3 participants experienced lip inflammation as a result of lauryl PCA. Flavoring agents (citral and vanilla) were also identified as causative agents in 2 case studies.

They also observed that lip plumping products contain ingredients that increase lip volume via vasodilation. This effect is achieved using ingredients with contact irritant effects, such as capsicum, or direct vasodilation effects, such as benzyl nicotinate. Although data are limited, the authors noted a case in which a 3-year-old child experienced a skin reaction after a kiss from their mother, who was wearing a lip plumper.

Allergenic ingredients in lip care cosmetics Original paper