Illustration of the various nail pathologies. From left to right. top to bottom : -healthy nail -ridged nail due to the nail ageing. The white marks are due to micro-impacts or vitamin deficiency. -ingrown nail. that has pierced the skin and caused painful swelling. -nail with psoriasis or fungus. The nail is yellow. detached and thickened. In most cases. the germ responsible is a fungus. dermatophyte. -damaged nail due to an impact. The nail falls off and grows back with transverse ridges which indicate how long ago the accident happened. -brown. stained nail which can either be a bruise. or a birth mark near the surface or. more seriously. a melanoma.