Answer
There are two occasions in Scripture when women wipe Jesus' feet with their hair. One is in Luke 7:38, the other in John 12:3. In the first instance, a prostitute wets Jesus' feet with her tears and wipes them with her hair. In the second, Mary the sister of Lazarus anoints Jesus with oil and wipes his feet with her hair. Probably, wiping feet with hair was an act of humble submission and devotion. Feet were dirty and smelly in the ancient Near East: roads were dusty, people wore sandals, and most people walked wherever they went. To wipe someone's unwashed feet with one's hair would have been rather disgusting -- all that dirt and sweat in your hair! -- and thus would show great devotion and humilty.
Of course, Jesus' feet may have been washed when Mary wiped them with her hair, so it may not have been quite as gross as when the prostitute did it. Still, it would have been a great act of humilty and devotion, and she may have chosen to use her hair specifically for this reason. Mary does seem to have been the only one who realized Jesus was going to die, so it is not unlikely that her grief and love overwhelmed her such that she engaged in this extravagent display.
Answer by Ra McLaughlin
Ra McLaughlin is Vice President of Finance and Administration at Third Millennium Ministries.