NAIL FORMATION AND SOME NAIL DISORDERS 4O9 there may be a minor traumatic element. It is essentially a disease of women and is seen more often in persons who like to keep their nails long. The disadvantages of a loose nail are that it feels uncomfortable, looks unsightly and the space below the nail is likely to collect dirt which is difficult to remove. The space is moist and warm and very easily becomes secondarily infected often with Gram-negative organisms. Pseudomonas aeruginosa infection is especially liable to occur and makes the overlying nail appear bluey-green or black in colour. Malodour may also develop and add to the patient's distress. A minority of these cases has undoubtedly been caused by nail cos- metics. Some of you will recall that several years ago a base coat was marketed which produced onycholysis in many persons (7). It could be shown that phenol from the base coat penetrated the nail and could be detected on its under surface. This resulted in a reaction either as a result of primary irritation or of an allergic nature and caused the separation. More recently the same change has been observed from the use of nail hardeners containing formaldehyde (8). There is no doubt that these preparations harden the nail but they are also liable to cause separation at the tips of the nails. In most cases encountered by the author the preparation had been used more frequently than recommended by the makers, but this was not always so. Once the nail comes loose it is very difficult to get it to re-attach. Another common nail sympton is splitting into layers or lameilar dystrophy (Fig. $). When a nail is made in three layers splitting might be expected to occur frequently. This is a simple explanation but may not be the whole answer. It is again a disease mainly of women, especially those who like to keep their nails long. Atmospheric conditions certainly play a part and repeated wetting and drying may be a factor. It is for this con- dition that nail hardeners are often used. A safe nail hardener is urgently needed. Gelatin by mouth has not proved of much value. Are there any other dangers from nail cosmetics? Nail varnish or polish is generally very well tolerated and seldom causes damage to the nail or its surroundings. Dermatitis of the eyelids and sides of the neck is well recog- nized as a contact dermatitis from resins in the varnish. Occasionally a nail will become yellow after the application of a varnish of a different hue. This is due to the leakage of a tint from the varnish into the nail. It is quite harmless but may cause great distress to a sensitive patient. This condition is difficult to reproduce experimentally. To avoid time wasting in the application of nail varnish, stick-on nail

410 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS dressings were marketed for a short time some years ago. They caused a great deal of damage very quickly and it seemed probable that this was due to their impermeability. Increased water content of the nail built up as a result of exclusion from the atmosphere so that the nail became soft and was damaged when the dressing was removed. Even so short a time as 48 h of use was sufficient to cause damage (9). False nails, if firmly attached to the nail, are likely to cause similar changes. False nails may be used to hide an underlying defect such as nail biting or psoriasis, but are often used simply for cosmetic purposes. Complete disruption of the nail can result in a few cases. These mishaps from nail cosmetics are very few compared to the damage caused by patients themselves! Nail biting is an extremely common habit and usually results in ugly ragged nails chewed right down to the hyponychium. Greater damage can be caused by biting the cuticle or by biting over the matrix. Pushing back the cuticle is carried out as a routine by many people. Carefully done this will do no harm, but over enthusiasm can cause regular cross white striations (Fig. 6) or cross ridging of the nail. Occasionally it may open up the potential space between the nail plate and dorsal nail fold and initiate chronic paronychia. Another habit which can produce a very ugly nail is playing with a nail, usually a thumb nail, with one of the other fingers on the same hand. This can be done quite un- consciously and produces a nail with a depression down the centre and a number of cross ridges extending from it almost to the sides of the nail (Fig. •). The nail matrix is responsible for the greater part of nail formation whichever method exists, and owing to its anatomical position is well pro- tected so that it is seldom damaged except by severe trauma. Occasionally, however, chemicals manage to get through to it and cause temporary or permanent loss of the nail (Figs. 8 and 9). This has occurred in recent years by accidental exposure to strong solutions of paraquat or diquat, dipyri- dilium compounds used as weed killers. The solutions are not generally available to the public but are used by farmers and foresters (10). The nail matrix is however often involved in skin diseases, especially psoriasis, and its protected position makes treatment very difficult. ACKNOWLEDGEMENTS My thanks are due to the photographic departments of Westminster and St John's Hospital for the photographic illustrations. (Received: 20th February 1971)