Allergic diseases, particularly asthma and asthma equivalents, are among the most frequent disorders seen in the pediatric clinic. Approximately 25% of children from developed countries have presented wheezing in recent years, and half of these children later experience major asthma attacks. Likewise, 25% of children between 8 and 11 years have at some time used beta agonists and at least 10% of them use preventive asthma medication. Prevention measures for allergic asthma include: 1) avoiding allergic sensitization; 2) avoiding the presentation of disease in sensitized patients; and 3) preventing symptoms after the disease has appeared. Allergic diseases have a multifactorial origin that includes genetic, perinatal, and specific and non-specific environmental factors. From a genetic point of view, asthma is a multifactorial and heterogeneous pathology with a variable degree of penetration and phenocopy. Allergy is more frequent among the offspring of atopic parents. Genetic variations in different chromosomes affect molecules and receptors involved in atopy: IgE elevation, Fce1 receptor and chromosome 11; IL-4 and chromosome 3; gamma interferon and chromosome 12; TcR a/d receptor and chromosome 14; TcR-beta and chromosome 7; and the main histocompatibility complex HLA I and II and chromosome 6. Likewise, it has been confirmed that genetic variants affect structures in the impact organs, such as the beta 2 receptors of IL-4 soluble receptors, which favor bronchial hyperreactivity. Recently, somatometric measures have been related (low weight and large head circumference at birth) with a later increase in IgE and the occurrence of asthma. The environmental factors most closely involved in the occurrence of asthma are: diet (early exposure to sensitizing foods); domestic, outside, and occupational seroallergens; pollution (particularly smoking and urban and industrial pollution); and infections, particularly viral infections. In the present study, the methods used for the early identification of children at risk are evaluated, as well as the role of the primary care pediatrician in the early detection of allergic children and the interventions that they carry out. Finally, an analysis is made of the preventive measures that should be taken in children at risk of allergic disease, particularly: 1) increasing awareness of health, 2) reduction of exposure to smoking. 3) reduction of urban and industrial pollution, 4) delayed introduction of certain foods, reduction in the level of domestic allergens, 6) control of infections, and 7) pharmacological measures designed to prevent the occurrence of asthma in children.