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How does someone’s beauty thing become their beauty thing?

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Thats the question were posing to celebrities and their beauty pros in our new series,Just One Thing.

Ive always had a signature hairstyle, even when I was in elementary school.

Back then, it was a ponytail with some very highbangs.

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Bilson during season one ofThe O.C.

It was a half-up situation, and I was like, I don’t do that.

And she said, No, youhaveto do that.

But my hair has always been undone.

I dont like put-together hair.

For me, its always been the messier, the better.

I guess you could call that a natural look, but my natural hair definitely needs some tweaking.

My routine is really badI don’t do anything to my hair unless I absolutely have to.

It brushes out, and its a miracle.

I want to do something crazy with my hair, like, weekly.

My hair changed completely when I became a mom [to daughter Briar Rose, 9].

It is so thin now; my ponytail is like the size of a penny.

Im already so low-maintenance with my hair, but I am definitely still in my mom-bun era.

But Ihavelearned how to curl my hair without it looking like a bouncy, put-together curl.

I can make it morebeachy, but I’m still not great at it.

[The look thats become my signature] really started onHart of Dixie.

I remember wearing some big Southern belle costume with crazy hair; I think there were twigs in it.

[My character] Zoe had the most fun hairstyles.

Zoes hairstyle with the twig dos and whatnot?

That was more me.

Bilson during season one ofThe O.C.

[In later seasons], they calmed Summer down a bit.

She wasnt asbronde, her hair wasnt as high.

She had such an arc, and she ended up more evolved.

I just feel like that tracks.

Read more about hair-centric celebrity interviews:

Watch Rachel Bilson’s makeup routine: