Lips turning black after kissing is usually caused by tiny bruises, also known as petechiae, which are formed when the pressure of the kiss ruptures tiny blood vessels in the lips. This is more likely to happen if the kissing is forceful or passionate.
These bruises are typically harmless and will fade within a few days. However, if the discoloration persists or worsens, it's best to consult a doctor to rule out any other underlying medical conditions.
If you're concerned about bruising your lips during kissing, you can try kissing more gently or using lip balm to lubricate the lips.
