Gene-environment interactions refer to how environmental factors like diet, lifestyle choices, and stress can influence how our genes are expressed in our cells. Our environments send signals to our over 10 trillion cells that interact with our 28,000 genes, turning them on, off, or changing their levels of expression. This results in each person having a unique response to their environment due to small genetic differences, as environmental cues cause our genetic "piano" to play differently for each individual. Our environments thus communicate with our genomes to determine traits like allergies, disease risks, and other aspects of our health and identity.