PRINCIPLES OF TOPICAL THERAPY:

Dermatology is unique in having such direct accessibility to the affected organ. This allows the use of topical treatments, which can avoid certain systemic side-effects.
A topical therapy consists of an active ingredient, an appropriate vehicle or base to deliver this, and often a preservative or stabilizer to maintain the product's shelf-life. Cosmetically acceptable products need to be found and patients should be instructed about their correct usage. Without this, compliance tends to be poor. Perfumed or scented products should be avoided.
Bases and their uses
Creams
These are a semisolid mixture of oil and water held together by an emulsifying agent. They need to have added preservatives such as parabens. They are 'lighter' and rub in more easily than ointments. They have a high cosmetic acceptability and are useful for topical treatments of the face and hands. Aqueous cream is particularly useful as a soap substitute.
Ointments
These are semisolid and contain no water, being based usually on oils or greases such as polyethylene glycol (water soluble) or paraffin (fatty). They feel greasy or sticky to the touch. They are the best treatment for dry, flaky skin disorders as they are good at hydrating the stratum corneum and they deliver an active ingredient (e.g. a steroid) more effectively.
If patients dislike the greasy nature of ointments, a cream is better than no treatment at all, but creams are less effective and do have to be used more frequently. A compromise may be to use a cream on the face and an ointment elsewhere (Table 23.16).
Lotions
These are based on a liquid vehicle such as water or alcohol. They are usually volatile and rapid evaporation promotes a cooling effect on the skin. They are useful for weeping skin conditions and are ideal for use on hairy skin (e.g. the scalp). The cooling effect can be a useful antipruritic. Alcohol-based lotions should be avoided on broken skin as they cause stinging.
Gels
These are semisolid preparations of high molecular weight polymers. They are non-greasy and liquefy on contact with the skin. They are useful for treating hairy skin (e.g. the scalp).
Table 23-16. Emollients commonly used in the UK
Greasy emollients Lighter creams
Diprobase ointment* E45 cream*
Oily cream Diprobase cream*
Unguentum Merck* Aveeno cream*
50 : 50 white soft paraffin/liquid paraffin Aqueous cream

*Trade names
page 1364

page 1365
Pastes
Pates contain a high percentage (> 40%) of powder in an ointment base. They are thick and stiff and difficult to remove from the skin. They are useful when a treatment needs to be applied precisely to a skin lesion without it smearing on to surrounding normal skin. An example would be dithranol in Lassar's paste (used on plaques of psoriasis) as dithranol will burn the surrounding normal skin.
Safety of topical steroids
Providing that preparations of appropriate strength are used for the body site being treated, these compounds can be used safely on a long-term intermittent basis (p. 1328). If potent steroids are misused they will cause skin atrophy manifest as striae, wrinkling, fragility and telangiectasia.
Problems with topical therapies
Systemic absorption may occur but only if very large areas of inflamed skin are treated topically and especially if the treatment is occluded with bandages or polyurethane films. Neonates are particularly susceptible to this owing to the relative increase in body surface area to volume.
Contact allergy to topical preparations is not uncommon and may be suspected by unusually resistant disease or by apparent worsening of a condition after application of a substance. It is more common with creams as it often the result of allergy to the preservative or emulsifying agent. Allergy can also be due to the active ingredient itself (e.g. neomycin or hydrocortisone).
Folliculitis can occur because of blockage of hair follicles. Creams and ointments should be applied to the skin in the same direction as hair growth to try to prevent this blockage. It is a particular problem with the use of ointments in hot weather (especially if under occlusive bandages) and a lighter cream may be more appropriate at this time.

CHAPTER BIBLIOGRAPHY
Champion RH, Burton JL, Ebling FJG (eds) (1998) Textbook of Dermatology, 6th edn. Oxford: Blackwell Scientific.
Harper J, Oranje A, Prose N (eds) (2000) Textbook of Pediatric Dermatology. Oxford: Blackwell Scientific.
Omary MB, Coulombe PA, Mclean I (2004) Mechanisms of disease: intermediate filament proteins and their associated diseases. New England Journal of Medicine 351: 2087-100.
Weedon D (ed) (2002) Skin Pathology, 2nd edn. Edinburgh: Churchill Livingstone.
UK PATIENT SUPPORT GROUPS (for full list see http://www.bad.org.uk/patientsindex.htm)
British Association of Skin Camouflage: c/o Resources for Business, South Park Road, Macclesfield SK11 6SH
DEBRA (Dystrophic Epidermolysis Bullosa Research Association): DEBRA House, 13 Wellington Business Park, Duke's Ride, Crowthorne, Berkshire RG11 6LS
Hairline International: 1668 High Street, Knowle, West Midlands B93 0LY
National Eczema Society: Hill House, Highgate Hill, London N19 5NA
Psoriasis Association: Milton House, 7 Milton Street, Northampton NN2 7JG
Vitiligo Society: 125 Kennington Road, London SE11 6SF