Why apply Vibuthi on the forehead?

The 'Vibhuti' [sacred ash], is even today, a near-patented product of the southern part of the country. Orthodox South Indians wear the "vibhuti" on various parts of the body, especially after a bath. Originally, 'Vibhuti' was derived as the highly potent 'Bhasma' [ash] arising out of 'Homams' performed with a plethora of medicinal herbs and leaves.

Sixteen varieties of medicinal leaves would be fed to cows. The dung of these cows would be collected after allowing sufficient time for digestion. The collected dung would then be formed into flat cakes and dried in the sun. 108 types of herbs, and twigs ['Samithi'] of high medicinal value would be used in the 'Homam' in which the dried dung cakes would be added. Six types of medicinal leaves would also be burnt along with these.

The residual ash, 'Vibhuti', retained the wonderful curative powers of its ingredients. It had excellent diuretic properties. For instance, smearing of "vibhuti" on the forehead after a bath in cold water would absorb the excess moisture in the head region and thus guard against sinus trouble.

Similarly, "Vibhuti" would be applied to other phlegm-prone areas such as the throat, chest, etc. Hence the practice of smearing 'Vibhuti' all over the body started off as a medicinal application, became a custom, and still later, became the identification mark for the Shaivites [ followers of Shiva cult] of South India.