There is growing awareness of the importance of the first 1000 days, the period from conception to the end of the second year of life, when the developing human is exquisitely sensitive to their environment.

During this period, exposure of the fetus or infant to stress, poor nutrition or environmental toxins can result in permanent changes to organ structure and/or function, resulting in increased susceptibility to disease over the lifespan.

The list of adult diseases that may be influenced by developmental programming has grown, as the understanding of this has expanded, to include obesity, diabetes, hypertension, cardiovascular disease, asthma and allergy, immune and autoimmune diseases, neurodevelopmental and neurodegenerative diseases/dysfunctions, changes in timing of puberty, infertility, cancers, and psychiatric and mood disorders.

Environmental exposures do not occur in isolation, and there is little information available about the combined effects of various chemicals, or the complex interactions with other factors such as stress, diet, heat, underlying medical conditions, genotype, gestation at the time of exposure, and fetal gender.