Setting aside the question of skin vs. hair for the moment, there is no method of applying the water that is prescribed in scripture. I believe Luther did say immersion is a great symbol of what is going on, i.e. the Old Adam dying and the new man rising. (NOTE: I am not saying Baptism is symbolic but that the method of applying the water is symbolic.) However, it was merely a preference of Luther. So, since Jesus prescribed no particular method, the method is left to freedom. One is free to immerse, or sprinkle three times to honor the Trinity, or to pour water continuously over the head. We are not free to change the element or the words however. There is be no doubt as to what God is doing in this means of grace.
And here is the main thing. The question of skin vs. hair puts the focus, the trust in the wrong place. From Luther’s Small Catechism we ask how can water do such great things? Certainly not just water, but the word of God in and with the water does these things, along with the faith which trusts this word of God in the water. For without God’s word the water is plain water and no Baptism. But with the word of God it is a Baptism, that is a life giving water, rich in grace, and a washing of the new birth in the Holy Spirit, as St. Paul says in Titus, chapter 3: “He saved us through the washing of rebirth and renewal by the Holy Spirit, whom he poured out on us generously through Jesus Christ our Savior, so that having been justified by his grace, we might become heirs having the hope of eternal life. This is a trustworthy saying.” (Titus 3:5-8)
I don’t know if you are doubting your baptism. I hope that these words are a comfort to you. It is not where the water fell on you that makes a baptism. Now, It seems the head is a logical place as it stands in for the whole. I suppose if someone were trapped under rubble and their head was inaccessible you would baptize what was exposed. So, here we see what is important concerning the comfort of baptism. It is the word plus the water that makes a baptism, not where the water hits the body. Where baptism is done in accord with Christ’s institution, there you can be sure that it is sure seal of God’s promise that he has washed you clean and claimed you as his own. When people argue over whether the water must touch the skin and not the hair, they are splitting hairs and robbing consciences of the comfort of the Gospel.
Hope this helps.
Pastor Gary Hall