One day, Hanuman noticed that Sita wore a red powder in the parting of her hair. Curious, Hanuman enquired, what it was that she was wearing. “Dear Hanuman, it is sindoor that I am wearing.” said Sita. “What is sindoor and why was it so important?” asked Hanuman. “Sindoor makes Lord Ram happy and would give Him a long and happy life.” explained Sita.
Hanuman thought for a long time. He realised that Sita also did it because she loved Ram and showed it by putting sindoor in her hair. I love Ram too, thought Hanuman, “And I’m going to prove it!’ So guess what He did? Well if Sita can put sindoor in her hair to show her love, He decided to cover Himself with it to show His love! He took the sindoor powder and smeared his whole body with it When He entered, He was completely red, His face, the nose, dhoti, everything was completely red. It looked as though He had taken a bath in the red powder!
Sita looked at Him in surprise and asked Him why he had covered himself in sindoor. Hanuman said, Matha! You are a Devi, a goddess. By putting a little sindoor in your hair, you can make Lord Ram happy and His life longer. But I am only His servant, His dasa, so I will have to do more than that. And that is why I had to cover my whole body with sindoor.”
This also shows the great love Hanuman had for Lord Rama. On hearing this, Lord Rama gave a boon to all his devotees that those who apply sindoor to Hanuman and observe hanuman pooja with sindoor would be blessed with longer and happy life.