Yang deficiency is a concept from traditional Chinese medicine. Yang-deficiency constitution is characterized by yang-qi deficiency and asthenia cold manifestation, and is mainly caused by genetic and environment factors. In terms of genetic factors, offsprings are affected by this defect through inheritance from yang deficiency constitution parents and as a result of poor healthcare during pregnancy. Environmental factors include adverse social conditions, unhealthy lifestyle, diseases, and medical misdiagnosis and inappropriate treatments. The phenotype is yang deficiency (Experimental Factor Ontology identifier EFO_0006817).