regrowth       
noun [ U ] uk/ˈriːɡrəʊθ/ us/ˈriːɡroʊθ/
 重新生长;再生之物
the act of growing again; something that has grown again
  the regrowth of forests after a fire 火灾后的森林再生  
hair regrowth 毛发再生  
It is often said that if you shave your head completely, the regrowth will be thicker. 人们常说,如果把头完全剃光,再生的毛发会更浓密。