When they first became a band on the Xfactor 2010 they were described as "five Justin Biebers". I can see where that came from as as well as being cute and innocent looking, the majority of them also had that side swept long hair thing made famous by JB.
1. Harry Styles
Luke the Kook. (Luke Pritchard from the Kooks). Fashion-wise as well, Harry dresses similar in style to Indie bands like the Kooks.
2. Zayn Malik
courtney rumbold in stooshe. The sides are shaved and he hair in the middle left long. Zayn then has the hair in he middle gelled up at the front. He has moved away from the original Justin Beiber style, however since justin had his new hair cut in 2012, they actually have the same cut now. Zayn's is better though.
3. Liam Payne
Liam looks like a country farmer in this picture, haha. He has similar hair to harry, unruly messy long waves. In some pictures I have seen, he has straightened his hair. He looks scarily like Jusin Beiber when he has straight hair..!
4. Niall Horan
looks dyed, I think he must have dark-ish blonde brown hair naturally). To me, he never really seems to fit into the group, even after being famous for like 2 years, he still looks really normal like they've just picked him up off the street. He often has the sideswept look as show above, or sometimes he gels up his hair in the middle to get a weird sort of pointy top or just some added height.
5. Louis Tomlinson
So all the One Direction hairstyles are quite high maintenance looks, there is a lot of hair gel and/or hair straighteners in use. It helps give them a together band image, which I guess is the whole point.. :)