The breed clubs do not recognize any other colors or patterns. This is because some colors come linked with genetic health problems not usually found in the breed. These include blue coloration, which is linked with a form of alopecia (hair loss or baldness), sometimes known as 'Blue Dog Alopecia'. Although this is heavily disputed by some organizations, it has been suggested that the health, hair and skin conditions are caused by the color pigment (melanin) clumping in the hair shaft itself. In terms of grooming, the French Bulldog requires regular nail trimming, brushing, occasional bathing, and ear cleaning. French Bulldogs are also prone to allergies, which can cause eczema on the body. Allergies can be caused by foods, insect bites, and French Bulldogs can also be frequently prone to hay fever and ophthalmic diseases. The most common colors are brindle, then fawn, with pieds being less common than the other colors.