The physiology of skin, hair, and nails is influenced by sex and age, reflecting distinct biological processes and health implications. Sex differences result in varying skin thickness, sebum production, and collagen density, which contribute to divergent aging patterns and susceptibility to dermatological conditions. Hair physiology also varies by sex, with hormonal influences like androgens in males contributing to patterns of hair growth and loss that differ from those observed in females. Aging affects hair follicle activity, leading to thinning and reduced pigment production, which presents differently across sexes. Nail physiology reveals further differentiation, as variations in the growth rate, strength, and texture between sexes can be attributed to hormonal fluctuations and genetic predispositions. Age-related changes in nails, including slower growth and increased brittleness, are universal but manifest differently across genders. This chapter highlights the physiological variations occurring in the skin, hair, and nails differentiated based on sex and age, while offering insights into their implications for clinical practice and personal care. By understanding these differences, strategies for maintaining dermatological health across the lifespan can be effectively tailored to individual needs.