Baby Steps on Challenging Ground: Understanding How Early-Life Irritability Impacts Mental Health Outcomes

Irritability is increasingly recognized as an important phenotype in early life. Since the groundbreaking longitudinal work in infants with difficult temperament by Chess and Thomas,1 conceptualizations of early irritability have grown and matured in the literature. Today, multiple measures of early irritability are available with a focus on dispositional anger, frustration, and negative reactivity. Additionally, investigators have mapped the normative developmental trajectory of irritability, which features a peak in temper tantrums in early childhood.2 This latter phenomenon creates an interesting challenge for research interrogating the clinical relevance of early irritability for later mental health in youth. How do we ascertain what is clinically meaningful in early life against the backdrop of wide individual and developmental variation in irritability?