The cortisol circadian rhythm and response to stressful stimuli are altered in children and adults with allergic disease, including asthma. It is not known whether these alterations precede or follow the onset of allergic disease.

We sought to evaluate the cortisol circadian rhythm and stress response among infants at risk for the development of allergic disease.

Infants with and without risk factors for allergic disease were evaluated at age 6 months. Saliva was obtained at 8 am, 2 pm, and 8 pm at home (n = 68) by parents when their infants were comfortable and in the clinic (n = 88) before and after their physical examination and vaccinations. Information regarding parental allergy and exposure to other children at home or in child care were obtained by questionnaire.

In multivariate analysis the circadian rhythm of cortisol was flattened because of the lack of the expected morning surge of cortisol, resulting in decreased diurnal variation of cortisol in infants of mothers with allergy (P = .035) or asthma (P = .002) or an asthmatic father (P = .022). The cortisol stress response was greater in infants of mothers with allergy (P = .045) or asthma (P = .039), those with fewer siblings (P = .066), and those not entering day care early in life (P = .017).

These alterations in both basal and stress levels of endogenous cortisol among infants predisposed to allergic disease might affect the development of allergic immune responses early in life through interactions with inflammatory mediators.