Smelly socks are socks that have acquired a strong odour due to prolonged wearing. Their odour, which is complex and remains the object of study, is a mixture of ammonia, fatty acids (in particular, isovaleric acid), and lactic acid. Odorous socks are a strong attractant for some animals, including dogs and mosquitos. They have proven useful in controlling the behaviour of these animals. Several technologies have been developed to incorporate materials into sock textiles which reduce or eliminate the strong smell.