Clinical review: The challenges of ageing skin

The ageing process

There are two forms of skin ageing: intrinsic and extrinsic. Intrinsic ageing represents the normal chronological process. It is unavoidable and genetically determined and leads to a number of functional changes, which are outlined in the box on the next page. In contrast, extrinsic ageing occurs as a result of cumulative exposure to environmental factors such as smoking, pollutants and UV radiation.

The impact of UV radiation on the skin is referred to as photo-ageing and involves the production of reactive oxygen species (ROS), which cause irreparable and cumulative damage to cellular DNA. ROS also increases the activity of collagenase enzymes, degrading both collagen and glycosaminoglycans, impairing the structural integrity of the skin and leading to the formation of wrinkles.

The skin contains various antioxidant systems that are capable of repairing damage induced by ROS. However, with advancing age, the body’s ability to deal with ROS declines, causing further damage. Although the number of melanocyte cells reduces with age, this reduction is uneven, particularly in sun-exposed areas of the skin. The net effect is the appearance of irregular pigmentation (solar lentigo or age spots).

Age-related problems

A recent systematic review that included 97 studies of community dwelling older adults
(over 60 years of age) identified the most common skin problems as:

• Androgenetic alopecia (up to 83 per cent prevalence)
• Seborrhoeic keratosis (up to 78.8 per cent)
• Solar lentigo (up to 71.6 per cent)
• Actinic keratosis (up to 69.4 per cent)
• Fungal infections (up to 64 per cent)
• Xerosis (up to 60 per cent).

Androgenetic alopecia

The underlying cause of androgenetic alopecia (male/female pattern baldness) is an age-related interruption of the normal hair growth cycle. This cycle involves three phases: anagen, the growth phase; catogen, during which growth stops; and telogen, the resting stage, when new hairs start to form before beginning to grow.

In androgenetic alopecia, there is miniaturisation of the pilosebaceous follicle, driven by elevated amounts of the androgen dihydrotestosterone. This miniaturisation not only shortens the anagen phase but also converts normal scalp hair into 

thinner and lighter vellus hair. In other words, hair not only becomes thinner and lighter but also fails to grow sufficiently to penetrate through the follicular opening, leading to baldness.

Unfortunately, there are limited treatment options for androgenetic alopecia in older adults. Although minoxidil is licensed for hair regrowth, its use is restricted to those under 65 years of age. Finasteride 1mg is an option for men. It works by inhibiting the enzyme 5-alpha reductase, which converts testosterone into dihydrotestosterone,
thus limiting follicular miniaturisation.

However, most of the efficacy data for finasteride comes from studies in those aged 18 to 48 years, and the drug is not available on the NHS. There is some evidence to suggest that finasteride may be effective in older adults, but as it is most effective before the onset of follicular miniaturisation, it is less likely to work in older men who have already experienced this process.

Seborrhoeic keratosis

Seborrhoeic keratosis, also known as basal cell papilloma, are harmless skin growths that have a ‘stuck-on’ appearance. The cause is unclear but might be related to genetics or even excessive sun exposure.

A recent Australian study observed how nearly a quarter of 15 to 30-year-olds had a seborrhoeic keratosis, which potentially supports a causative role for sunlight. Although benign, seborrhoeic keratosis lesions can enlarge, catch in clothing and subsequently bleed and result in a secondary infection. Consequently, patients often request that they are removed either by cryotherapy or cut off with curettage.

Solar lentigo (age or liver spots)

Solar lentigo (plural lentigines) is related to excessive exposure to sunlight. Since these lesions are benign, no treatment is required.

Actinic keratosis

Actinic keratoses are markers of chronic sun damage and therefore normally appear on areas of the body such as the face, scalp and the dorsum of the hands. In the earliest stages, lesions are best felt rather than seen and the skin is often described as feeling like sandpaper.

These are premalignant skin lesions with the potential to undergo malignant transformation into a squamous cell carcinoma. However, the rate of conversion for an individual lesion is less than 1 per cent a year, although this risk increases when there are more lesions present.

Individual lesions can be treated with liquid nitrogen cryotherapy, but in practice, many older adults experience
actinic damage over a large area of skin, such as the scalp (known as ‘field changes’). With a higher number of lesions and within this actinic field, it is impossible to predict which ones might undergo malignant transformation. 

Consequently, it is recommended that these actinic fields are treated. Appropriate therapies include 5-fluorouracil, imiquimod or diclofenac gel. In most cases, field-directed therapy reduces the number of lesions. It is also important to recognise that some lesions undergo spontaneous remission. Once they have resolved, the use of sun protection measures (e.g. broad spectrum sunscreens, avoiding the sun between 11am and 3pm) will help to minimise the risk of developing new lesions.

Fungal infections

Opportunistic fungal infections reside within the epidermis. In younger adults, shedding of epidermal cells prevents such organisms from becoming established. In contrast, older adults are more susceptible to infections because of a reduction in the number of Langerhans cells and a decrease in the replacement of keratinocytes.

While such infections can be managed with systemic antifungals, the use of these drugs in older adults can be problematic. For example, all systemic azole antifungals are hepatotoxic, so liver function tests are needed before commencing treatment.

There is also an increased risk of drug inter-actions, especially since older adults tend to be on polypharmacy regimens. Alternatively, topical azoles or allylamines (e.g. terbinafine) can be used.

Xerosis (dry skin)

The combination of lower production of intercellular lipids, NMF and sebum excretion decreases the water content of the stratum corneum, leading to dry skin.

Once the skin becomes dry, it can crack and these cracks provide an entry portal for micro-organisms and cutaneous infection. Numerous studies have shown that the skin’s pH increases from being slightly acidic towards neutral in older adults, which in turn also impairs the skin’s barrier function.

As older adults feel the cold more than younger people do, several common practices tend to exacerbate xerosis. For example, the use of fan heaters and other sources of low humidity heat like central heating causes further drying of the skin. In addition, taking a hot bath or shower and using soaps and detergents will strip the skin of its natural lipids. This is particularly troublesome for older adults, whose skin naturally produces fewer lipids, again worsening dryness. Using soap-free cleansers with a pH of four to five and taking warm rather than hot baths and showers helps to minimise this effect.

Asteatotic eczema

This is the most common form of eczema in older adults. It presents with dry and inflamed areas of skin, often on the shins. The condition tends to be worse during the winter months and is largely due to skin dryness, although diuretics, hypothyroidism and malignancies are also potential causes.

Asteatotic eczema can be managed with the use of emollients, together with mild to moderate potency topical steroids where inflammation is a prominent feature. Patients should also be advised to wash with emollient products and avoid soaps. Emollients containing humectants such as glycerol and urea attract and hold water in the stratum corneum, replicating the effect of NMF.