Authors : Dr. Rabiya A hameed .
 

Abstract

Aging is a biological process that can be of two types

1. Intrinsic aging
2. photoaging

While intrinsic aging is an internal process,photoaging is premature and is due to sun ultraviolet exposure. Various retinoid natural and synthetic are explored and evolved for the treatment of aging and many has shown clinical and histological improvement, but most of the product studies are carried out on photo aged skin. However the studies carried out is mostly on tretinoin for photoagedskin . A considerable results have been appreciated in the treatment of retinoids but the reaction to these chemicals have limit their use in patients such as scaling of skin, burning sensation, dermatitis and irritation.

Mainly the reactions are more with use of tretinoin and tazarotene whereas other group of retinoids is less irritating such as retinaldehyde and retinol. Many advancements are achieved in the newer drug delivery system to minimize the irritating characteristic of the molecules eg. Nanoparticles. However there are much to be studied and elaborated to confirm the advantages in the delivery of topical retinoids.
 

Introduction:

The skin is known as a cutaneous membrane and it covers the external surface of the skin and is the largest organ of the body – it protects all the other organ from the external environment. The skin consists of multiple layers basically divided into three layers: epidermis, dermis and the subcutaneous tissue. The epidermis contains four principle cells keratinocytes, melanocytes, macrophages, tactile epithelial cells out of which the keratinocytes in the epidermis is almost 90% arranged in 4-5 layers.

The dermis is the second layer which consists of dense irregular connective tissue containing collagen and elastic fibres. This layer has a great ability to stretch and recoil itself. Apart from protection the function of the skin includes sensory detection, excretion, immune response, regulation of body temperature. The major role played is by stratum corneum which consists of 25- 30 layers of flattened dead karatinocyes which are extremely thin and without nucleus. The cells in this layer are arranged as a jigsaw puzzle that helps to hold the layers together. The multi-layered stratum corneum helps to protect the deeper layers from injury and any microbial invasion. The constant exposure of skin to friction increases the cell production. The process of skin rejuvenation takes place in this way throughout the layers and this process slows down with age making the skin more drier, less elastic and thinner.
 

The process of aging

Aging is a biological attrition at cellular level, the capacity to multiply and the elastic property reduces considerably. The number of pigment containing cells reduces such as melanocytes; the aging skin looks thinnerand more fragile. The connective tissue changes resulting in compromised skin strength. The elasticity is reduced this is known as elastosis. The vessels in the dermis become more fragile and are easily bruised. The oil capacity of the skin to produce sebum and oil reduces considerably resulting in dermatitis.

The subcutaneous fat layer thins out which directly affects the capacity of the skin for insulation and padding which increases the chances of injury and reduces the ability to maintain body temperature. The sweat glands produce less sweat this directly affects the skin ability to keep the body temperature cool which therefore increases the chances of heat stroke. This is a genetic alarm implanted in the genes of each and every species. There is cumulative damage to the genetic system due to aging the protein and its production is highly compromised. Capacity for vitamin D synthesis reduces. This in turn leads an organism to premature aging and death.
 

What is photoaging?

As skin ages and looses its youthful appearance wrinkles appears around the eyes and throughout the body slowly and gradually. While some of these factors are natural there are few factors caused by sun and can be avoided. These are harmful radiations from the sun which are of two different types UVA and UVB. When ultraviolet radiation hits the skin it increases the production of melanin pigments which in turn gives a tan skin, this is a process of the skin to protect itself from harmful radiation penetrating deep into the dermis.

The UVB rays have a shorter wavelength than UVA, the UVA rays are the major culprits which are majorly associated with photoaging. These rays penetrate deep into the dermis where they damage the production of collagen and increases the amount of abnormal elastin fibres. The increase in abnormal elastin fibres result in the production of enzyme metalloproteinases (MMP’s). These enzymes which helps in rebuilding collagen often malfunction and degrade the collagen, resulting in incorrectly rebuilt skin. Thus the MMP’s have the capacity to completely degrade even mature collagen and impairs the production of new collagen.This brings wrinkles and sagging to the skin.

Repeated exposure causes age spots which are called “Liver spots” which are nothing to do with the liver. Ultra violet radiation activates multiple cytokines and growth factor receptors. This includes tumor necrosis factor (TNF), epidermal growth factor receptor (EGF-R), interleukin 1, platelet activating factor, platelet derived growth factor and many more.
 

Retinoids

Retinol, which is vitamin A, was discovered way back during the World War 1 where the research has shown that its deficiency causes follicular hyperkeratosis and xerosis. The family of retinoids includes retinoic acid, retinaldehyde, retinyl esters and many synthetic derivatives. Retinol is a twenty-carbon ring