Intrinsic ageing and extrinsic ageing are terms used to describe cutaneous ageing of the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

and other parts of the

integumentary system The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves ...

, which while having

epidermal The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...

concomitants, seems to primarily involve the

dermis The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...

. Intrinsic ageing is influenced by internal physiological factors alone, and extrinsic ageing by many external factors. Intrinsic ageing is also called ''chronologic ageing'', and extrinsic ageing is most often referred to as ''photoageing''.

Causes and effects

The effects of ''intrinsic ageing'' are caused primarily by internal factors alone. It is sometimes referred to as chronological ageing and is an inherent degenerative process due to declining physiologic functions and capacities. Such an ageing process may include qualitative and quantitative changes and includes diminished or defective synthesis of

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

and

elastin Elastin is a protein that in humans is encoded by the ''ELN'' gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the bod ...

in the dermis. ''Extrinsic ageing'' of skin is a distinctive declination process caused by external factors, which include ultra-violet radiation, cigarette smoking, air pollution, among others. Of all extrinsic causes, radiation from sunlight has the most widespread documentation of its negative effects on the skin. Because of this, extrinsic ageing is often referred to as photoageing.Uitto J, Fazio MJ, Olsen DR: Cutaneous aging: Molecular alterations in elastic fibers. ''J Cuta Aging & Cos Derm'' 1(1):13-26, 1998.

Photoageing Photoaging or photoageing (also known as "dermatoheliosis") is a term used for the characteristic changes to skin induced by chronic UVA and UVB exposure. Tretinoin is the best studied retinoid in the treatment of photoaging. The deterioration ...

may be defined as skin changes caused by chronic exposure to UV light. ''Photodamage'' implies changes beyond those associated with ageing alone, defined as cutaneous damage caused by chronic exposure to solar radiation and is associated with emergence of neoplastic lesions.

References

Physiology Senescence