"I have a lot of hair" 可以说成 "I have thick hair" 或 "I have a thick head of hair".
"Thick" 这个词的意思是"厚的，浓密的"，指头发稠密。
例句：
"She has thick, curly hair." (她有卷曲浓密的头发。)
"He has thick, black hair." (他有黑色浓密的头发。)
"I've always been jealous of my sister's thick head of hair." (我一直嫉妒我姐姐浓密的头发。)