The aging of the skin and various other factors lead to the sagging of the skin and a loss of elasticity and firmness in its complexion. Some of the factors that influence the sagging of skin are:

Aging: During the aging process, the skin produces less collagen and elastin, proteins responsible for maintaining elasticity and firmness.
Sun exposure: Prolonged sun exposure can damage collagen and elastin fibres, expediting the breakdown of these proteins and contributing to skin sagging.
Weight fluctuations: Rapid weight loss or gain can cause stretching to the skin and result in sagging.
Genetics: Some individuals may be predisposed to have less elastic and firm skin, causing the individual to be more prone to sagging.
Personal factors: Some individual factors include poor nutrition, smoking, alcohol consumption, and lack of skin care.