General Information: The following is from an extraordinary book by Kasma Loha-unchit, It Rains Fishes: Legends, Traditions and the Joys of Thai Cooking, published by Pomegranate Artbooks, 1995.
Both the exceptionally fragrant fruits and leaves of the kaffir lime tree play important roles in Thai cooking, imparting unique flavors that have become identified with the cuisine. Any Thai cookbook that alludes to the use of citrus leaves really means kaffir lime leaves, the only citrus leaves used with regularity in a wide array of favorite Thai dishes. The luscious perfume and striking flavor of the leaves cannot be easily substituted with other kinds of citrus leaves. They are worth seeking, as their special attributes are irreplaceable.
The kaffir lime fruit approximates the size of a Western lime. The fruit is dark green in color and has a bumpy surface. Through the juice is seldom used in cooking, the peel of the fruit, with its high concentration of aromatic oils, is indispensable in many curry pastes and is one reason why Thai curries taste refreshingly unique. The zest also imparts a wonderful piquant flavor to such delectable favorites as fried fish cakes, and it blends in powerfully with such spicy, chili-laden stews as "jungle soup" (gkaeng bpah). Because it's strong flavor can over power the more subtle ones in a dish, the rind should be used sparingly, grated or chopped finely and reduced in a mortar with other paste ingredients until indistinguishable.
Besides supplying great flavor ingredients to enhance food, kaffir lime is also used as a indisputably effective cleanser, natural deodorizer and add a sparkling scent, like sweet bouquet of citrus blossoms, and each scratch of the zest releases another installment of refreshing perfume.
Kaffir lime shampoo leaves the hair squeaky clean and invigorates the scalp. It is believed to freshen one's mental outlook and ward off evil spirits. Kaffir lime has also been used for ages as a natural bleach to remove tough stains.
In folk medicine, the juice of kaffir lime is said to promote gum health and is recommended for use in brushing teeth and gums. The essential oils in the fruit are incorporated into various ointments, and the rind is an ingredient in medical tonics believed to be good for the blood. Like lemon grass and galanga, the rind is also known to have beneficial properties for the digestive system.