"Slight irritation" refers to a small but bothersome feeling of annoyance or dissatisfaction that may bother someone only a little bit. Full definition
The other slight irritation is just how similar the majority of the areas look. (thexboxhub.com)
It is in no way unusual phenomena and will happen multiple times over the course of your baby's growing up due to various reasons: allergies, cold, slight irritation, etc.. (followmum.com)
Except upon the introduction of formula or solid foods, any variance in the color of baby's stools also indicates that something's off — from a slight irritation to a dangerous disorder. (babyreference.com)