Skin and Aging

The skin structure and function changes throughout the human lifespan. The changes described in this section should be seen as inevitable biological processes, although it may be possible to slow down ageing, no one has yet worked out how to stop it happening altogether! Table below shows some terms which may be used to describe skin growth and skin death.

Skin Growth and Skin Death

Skin Death

Definition

Atrophy

Skin shrinking or reducing due to loss of cells either in size or number. This can be either through lack of use (disuse atrophy) or old age (senile atrophy)

Necrosis

Premature, pathological death of tissue caused by trauma, infections or toxins

Gangrene

Tissue necrosis resulting from insufficient blood supply

Skin Growth

Definition

Hyperplasia

Multiplication of cells

Hypertrophy

Enlargement of existing cells

Neoplasia

Tumour composed of abnormal non-functional tissue

Pre-birth

During embryogenesis, layers of cells known as germ cells are formed. Skin will eventually be formed by the cells in two of these layers; the ectoderm forming (amongst other structures) the epidermis and the mesoderm the dermis.

The baby is protected in utero by a thick layer of vernix caseosa, a very effective greasy substance which protects the infant’s skin from the watery environment of the amniotic fluid. The words vernix caseosa come from a Latin derivation, vernix, meaning ‘varnish’ and caseosa ‘cheesy’. The vernix is composed of sebum, which is secreted from the baby’s sebaceous glands from around 20 weeks, and skin cells as they desquamate. Further protection is provided by the fine, downy hair known as lanugo. This falls out soon after birth to be replaced with vellus and terminal hairs.

At birth

If a baby is born after its due date, the vernix caseosa would have mostly gone which means the skin tends to be dry and peeling as it has not been effectively protected in the watery environment of the womb. If a baby is born prematurely, its skin will be more vulnerable as it would not have had chance to mature completely, making it more prone to infection and trauma. This being said, the skin of a newborn is generally quite vulnerable due to the immaturity of the skin barrier. It has not developed a complete flora and fauna, so does not have full protection of the commensal bacteria nor has it developed the acid mantle. For the first 6 weeks of life, it is recommended that water alone is used to cleanse the skin. Subsequently, any products that are used should have minimal levels of perfume and colourants in them. Bland emollients (see Chapter 5) may be helpful if a baby’s skin gets dry.

Babies in neonatal units have particularly vulnerable skin. A survey carried out at the University of Southampton suggests that despite this fact, many neonates have their skin overly cleansed and frequently damaged with tape and dressings.

Post-birth/early months

There are a number of skin changes in the early months which can be considered ‘normal’ that do not usually require any intervention except reassurance.

Milia

These are tiny white spots which appear over the nose and face of babies; they are common. Their formation is probably related to the stimulus of the sebaceous glands which become temporarily blocked. There is no need to squeeze them as they will resolve of their own accord. The sebaceous glands become small and inactive soon after birth and as they do the milia resolve. The sebaceous glands remain inactive until puberty.

Mongolian blue spot

These are also relatively common in babies of Indo-Asian or Afro-Caribbean origin and occur in over 90% of children of Mongolian extraction. They consist of a blue grey patch on the skin which often occurs on the sacrum but can occur anywhere on the body. The skin surface is normal. The cause is thought to be elongated melanocyte precursor cells in the dermis. They can be mistaken as trauma from non-accidental injury, so should be documented in the notes. For most children these patches will fade as they get older, some however will persist into adulthood.

Benign acquired melanocytic lesions

Both freckles and lentigo can be described as benign acquired melanocytic lesions. Freckles are areas of skin where melanocytes are seen to be more active than in neighbouring areas. As a result, small (less than 5 mm in diameter), flat areas of pigmentation appear, generally scattered over the face, neck and arms, appearing in a variety of shades depending on the individual and the time of the year (darker in summer). Lentigo (plural being lentigenes) are also flat and a similar variety of sizes as the freckles, but they do not vary with sun exposure. Unlike freckles where there is no increase in the number of melanocytes, in lentigo there are.

Congenital melanocytic naevi

These lesions may be small or giant and occur in approximately 1% of births. The surface of the lesion may be smooth or rough and warty; there may be one or more hair follicles in the lesion. Giant congenital melanocytic naevi (those that cover a large area of the body and may be accompanied by thousands of smaller lesions) are associated with malignant melanomas and parents will need careful counselling about what action to take. Sometimes, the lesions are too large to consider surgical excision and grafting.

Vascular naevi

Vascular naevi are caused by dilated and tortuous, but otherwise normal blood vessels. Where capillary vessels are involved, a superficial or deep type may be described.

The superficial capillary naevi are caused by abnormal dilated vessels in the superficial dermis leading to salmon-coloured patches often on the face that will fade quite quickly. They are relatively common, occurring in approximately 50% of all neonates. The deeper capillary naevi are known as ‘port wine stains’, and because the vascular abnormality extends deeper into the dermis, these do not resolve and may even extend throughout life. The colour of the patches varies from pale pinkish red to dark purple; the colours will deepen with age. These changes can be associated with intracranial vascular changes and neurological pathology, so any child with a facial port wine stain should be investigated.

Arterial naevi

Otherwise known as superficial angiomatous naevi or strawberry birth marks, these occur in around 10% of children by the age of 1. Commonly, they start growing within a few days to a few weeks of birth and are usually relatively soft and irregular in outline. Sometimes there is a deeper component to these naevi where the subcutis is involved, in these instances the changes may lead to a distortion of normal anatomy. Growth of the lesion usually stops at around 6 months and resolution is usually spontaneous and complete, although if the lesion was particularly large, lose skin or atrophy may be left. The following rule of thumb is usually quite accurate:

Forty percent are gone by the age of 4 years; 50% by 5 years; 60% by 6 years; 70% by 7 years; 80% by 8 years and 90% by 9 years. (Graham-Brown and Bourke, 1998).

If the lesion interferes with feeding, breathing or sight, treatment may be recommended. For smaller areas, this is likely to be a steroid injection, but other options may be necessary including laser therapy. These types of naevi usually occur on the head, neck, buttocks or perineal areas. If they are associated with the lower back, sacrum or buttocks, a scan is usually recommended to exclude problems of tethering of the spinal cord.

Physiological jaundice (icterus neonatorum)

At about 2 days of age, parents may notice that their newborn is a yellowish colour. This is quite normal and results from the breakdown of the excess red blood cells that the child needed when they were in utero. As the child breaths following delivery, it no longer has any need of these red blood cells, so they break down leading to high serum bilirubin levels and the consequent yellow colour. This type of jaundice should not be confused with pathologic jaundice which occurs within 24 hours of birth and may be indicative of ABO or rhesus incompatibilities.

Puberty

Puberty is the time at which reproductive organs become functionally active. In both males and females, it is accompanied by the development of the secondary sexual characteristics including the growth of pubic hair and axillary hair and facial hair in boys. These changes are due to a large increase in the secretion of gonadal sex hormones. Androgens have a powerful effect on the hair follicle stimulating the sebaceous gland that has lain dormant since shortly after birth. This leads to an increased production of sebum causing teenage skin and hair to be greasier than prior to puberty. For some, this change in the sebaceous gland functioning will mean the appearance of acne. Most teenagers experience comedones, others will experience more extreme acne with pustule or even nodule formation. The apocrine glands are also stimulated leading to the experience of body odour for the first time.

Teenage years are also a time when young adults start to take a real interest in their appearance and is a good time to encourage healthy skin behaviour, including protection from UV radiation.

Pregnancy

Hormonal changes throughout the menstrual cycle can influence the skin and hair for some women. It is during the second half of the menstrual cycle, following ovulation when the progesterone levels peak, that women notice changes in their skin and those with a skin condition can experience an exacerbation.

During pregnancy some specific changes do occur, specifically a deepening of the normal pigmentation of the nipple, the areola, the genital area and the midline of the abdominal wall. Following delivery this pigmentation will fade, but seldom back to the usual colour. For a proportion of women (around 70%), the second half of pregnancy sees chloasmal pigmentation which is characterised by an irregular, sharply marginated area of pigmentation which develops in a symmetrical pattern over the cheeks and/or forehead. It is also common for women to see their moles darken whilst pregnant and it is also possible for new moles to appear. It is advisable for pregnant women to take additional precautions when going out into the sun; they should wear a hat and use a high factor sunscreen.

Vascular changes mean that women notice flushing of the palms of the hands and spider naevi appear on the face, upper trunk and arms. Oedema of the lower legs and increased appearance of varicose veins occur due to a rise in venous pressure caused by the increased pressure of the growing foetus impeding venous return. Dermal changes include stretch marks which occur due to weakened tensile strength of dermal fibres (caused by the increase corticosteroid output) and the stretching of the skin due to the growing foetus. A study carried out in Southern India showed that nearly 80% of women experienced stretch marks following pregnancy (Kumari et al., 2007). Marks appear as raised reddish/purple lines during and just after pregnancy, which fade to more skin- coloured slightly depressed shiny lines. Avoiding stretch marks during pregnancy may be down to genetic good
fortune; however, the following strategies may help decrease the likelihood of stretch marks or at least their severity:

• Gradual and moderate weight gain during pregnancy (a woman with a normal body mass index should aim to gain between 25 and 35 lbs during pregnancy.);
• Gentle exercise;
• A Cochrane review considered studies that looked at topical products which might alleviate stretch marks. The review highlights one product containing Centella asiatica extract, alpha tocopherol and collagen–elastin hydrolysates, which when compared to a placebo was associated with women developing fewer stretch marks. A second study suggested that a product containing tocopherol, panthenol, hyaluronic acid, elastin and menthol was associated with women developing fewer stretch marks. But this study did not include a control and the improvements may have been associated with the massage (Young and Jewell, 1996).

Old age

As humans get older, the skin becomes thinner, less elastic, drier and more finely wrinkled. The degree to which the skin becomes visibly aged is related largely to genetics and photo-ageing. In other words, wrinkle formation is determined by the traits inherited from parents and the extent to which someone has exposed themselves to sunshine over their lifetime. Intrinsic ageing describes the natural biological processes which it is not possible to control and extrinsic ageing the impact that the environment and exposure to it has on the skin. It is possible to get a sense of the impact of extrinsic factors by comparing the skin of a sun-exposed and non-sun-exposed site. In an elderly person, particularly, there is a marked difference between the texture and colouring, the former being much smoother and less wrinkled.

The changes highlighted in Table shown below mean that older skin is increasingly sensitive and less able to cope with external stressors on the skin. Thus the skin has less innate ability to cope with external agents such as perfumes in topical products, extremes of temperature, urine and faeces. Overexposure to UV radiation is responsible not only for the effects of ageing but also more worryingly for skin cancers. Basal and squamous cell carcinomas are both closely associated with prolonged sun exposure and whilst they are rarely life threatening, they can be locally destructive and need to be properly diagnosed and treated. Malignant melanomas are also associated with sun exposure, although burning is generally thought to be a high risk factor.

Skin Changes Caused By Aging

Changes in the skin

Consequence

Epidermal turnover slows

Thinner skin

Less effective barrier function

More prone to infection/dryness

Less flexible and tough collagen

More prone to wrinkles and sheering

Less evenly distributed melanin

More prone to sun damage

Fewer sweat glands

Less effective temperature control

Less sebum production

Increased skin dryness

Conclusion

The skin provides humans with a flexible and dynamic outer layer. Its complex structure and function create a unique environment which protects the inner functionings of the body and provides an incredible interface with which to interact with the outside world. This chapter has formed the basis of a biological understanding of the skin; the rest of the book will look at what happens when skin fails, from a number of different perspectives.