Kalva is a red-yellow coloured holy thread, sometimes with knots or amulets, mainly found in India. It is also known as kalava, Mauli, moui, raksasutra, pratisara (in North India), kaapu, kayiru or charandu (in South India). A kautuka is traditionally believed to be protective or apotropaic (protection from the evil eye). The “vaids” (ancient doctors) of the past understood that a pathogenic outbreak could wipe out the whole community and compliance by all was necessary. So in order to enforce compliance, it was integrated into religion.
According to an interesting legendary tale, when Lord Vishnu incarnated as Vamana avatar, He pushed King Bali into the underworld. It is believed that he tied kalava on the wrist of Bali, to grant him immortality. That began the practice of tying a red kalava on the wrist of people, to grant them long lives.
There are also a few scientific reasons for tying kalava, It is for immunity from pathogenic(harmful) bacteria. The skin microbiota, i.e. the organisms that reside on our skin are usually non-pathogenic, and either commensal (are not harmful to their host) or mutualistic (offer a benefit). So whenever there is an infestation by pathogenic(harmful) bacteria, the skin microbiota helps in resisting the spread of the harmful bacteria. The kalava provides an exclusive breeding site for the beneficial micro-organisms. In the ancient days, there was the absence of antibiotics, a strong defence was the best offence. In those days any outbreak could have scaled up to epidemic proportions.
Vata or Vayu is crucial to mobilize the function of the nervous system. Pitt or bile for digestion and supply of blood and energy to various parts of the body. Kapha or phlegm is the carrier of nutrients into the arterial system. It is believed that tying three knots in the Kalava creates enough pressure on these veins to keep your body free of any disease related to these three constituents. From the ancient time priests believe that our complete body is control by the wrist vein. So, if we tie kalava on the wrist, it helps regulate the body’s blood circulation.