Alliteration is the repetition of the same consonant sound at the beginning of words in close proximity.
In "human hair," the initial sounds of the words ("h" and "h") are the same, but the vowel sounds are different. To be alliteration, both the consonant and vowel sounds should be repeated.
Here's an example of alliteration: "big, bold, beautiful" (all words start with the "b" sound).