SOME DIFFICULTIES OF TOPICAL TREATMENT IN DERMATOLOG¾ 31 itch sensitivity varies moles and papillomas become tag-like or peduncu- lated on such areas of skin as the eyelids, neck (as seen in menopausal women), groins and axillae simply because, in some way, the skin is different there. Absorption of medicaments is also much influenced by the thickness of the horny layer as on the palms or soles compared to thin facial or flexural skin. The fundamental biochemical and enzymic differences, however, have still largely to be determined. DISORDERS OF KERATINIZATION The integrity of the main epidermal barrier (the stratum corneum) depends mainly upon the intact linear protein (keratin) chains and their firm cross4inking by the strong disulphide (cystine) and weaker hydrogen and salt links of individual amino acids. The protein manufacture in the lower viable epidermal cells, and the degradation in the outer dead horny layer is enzymically determined. The integrity, however, also depends upon an adequate water content replaced from sweat in and between the keratin chains to keep the skin supple, in turn protected by a layer of oily sebum which prevents evaporation. Patients with inherent abnormalities of keratinization, and varying capacity to retain water, are particularly liable to functional disturbance from physiological, environmental or disease factors. They may be seen as a spectrum from severe types of ichthyosis, the harlequin foetus whose skin is incompatible with life, through grades of ichthyosis to the milder forms as seen in most atopics (subjects of the eczema-asthma-hay fever- syndrome) and senile skins, to mild skin xerosis and keratosis pilaris where the defect is seen like a nutmeg grater at hair follicles of the arms and legs. The group to be treated also includes dry states of the skin con- valescent from inflammations such as eczema. These skins make up a large community who often require topical symptomatic therapy. THE HYDRATION OF KERATIN Reduction of water content by evaporation or climatic conditions when a cold dry spell causes a rise of barometric pressure and dew point (where gaseous moisture condenses) produces dryness, chapping, and stiffening of the keratinous horny layer in these susceptible skins. In the background parade many minor disorders. Among these are the superficial dry flaky eczemas of the face, pityriasis alba (the "tetters") as in children, chapping of wrists or hands especially where wet work increases evaporation, as in housewives or behind the knees in children,

32 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and dry, chapped lips in mouth breathers, unconscious persons, or those who continually lick their lips as a nervous habit. Splits may occur in thin and brittle skin behind the ears, or sides of the mouth or vestibule of the nose in those who habitually blow the nose with rigour secondary growth of bacteria in these sites are continual sources of cutaneous infection in the neighbourhood, as occurs with boils. Nail affections include fissuring of the nail cuticles or "hang nails" with secondary nail fold infections, and brittleness of nails similar but more pronounced nail changes with tenderness, discolouration and the collecting of warty keratinous debris has occurred through occlusive dis- turbance of hydration with artificial finger nails. Solvents used for hand cleaning in industry allow dehydration through the removal of the waterproofing sebum, as also do alkaline agents and washing powders. SUSCEPTIBILITY TO IRRITANTS Abnormally keratinized or dehydrated skin is also susceptible to mechanical trauma and to frictional and chemical irritants because of its inelastic state, and because of the ease of damage to the keratin molecule. Weak chemical irritants of everyday life, such as alkalis in washing agents or cement and reducing bleaching agents, easily disrupt the strong disulphide molecular chain links in dry skins, in the same way that oxidizing agents will effect the weaker hydrogen links. Later penetration of chemicals or bacteria are then able to provoke allergic or persisting eczema reactions, the patient presented with a chronic relapsing patchy eczema. Other examples of these effects are winter eczema on the outside of the legs of those who over-bath, are soap intolerant and who wear heavier clothing in the winter the asteatotic eczema of the man who is over- scrupulously clean and is constantly washing his hands the squamous eczemas of the palms in those using hand tools in industry and the chronic patchy industrial eczema of those constantly exposed to weak irritants, alkaline materials, oils, solvents, or wet work. The frictional effects of wearing apparel are also increased, as are degrees of itching by dry spicules of projecting keratin and abnormal irritability of the erector pili muscles with cold or nervous tension which causes a more prominent elevation of the hair and follicle. Static electricity