Reese Witherspoon's eldest child, Ava Phillippe, admits she's battled with anxiety for years.

The 24-year-old college student - who is studying social welfare at UC Berkeley - has spoken out about her struggles with her mental health in a Q+A with her Instagram followers.

Ava - whose father is actor Ryan Phillippe - said: "I've dealt with anxiety for as long as I can remember, and it was especially intense for me as a kid and teenager."

Offering her advice to fellow sufferers, whilst acknowledging that what works for one person may not necessarily help another, she replied to one user: "Don't invalidate your feelings.

You have every right to feel however you do, even if it seems weird to others, and being hard on yourself won't help you feel better or find a solution."

Sharing another method, she continued: "Note 1-3 things you can smell, touch, hear, etc… in the moment and remember: this feeling will pass, even if you have to ride it out for a while."

Ava - who is a big sister to ‘Legally Blonde’ star Reese and Ryan's 19-year-old son Deacon - picks her skin whenever she is feeling anxious, but it's something she is learning to control as she gets older.

She said: "It's just so tempting for some reason, but I think I've been better about not doing that as I've gotten older."

Ava's father has battled with his mental health, too, and recently opened up about getting sober.

The 49-year-old actor admitted the "clarity and spiritual connectedness" he has experienced since giving up drugs, including nicotine, have left him feeling "real good" but didn't state how long he has been clean.

Sharing a mirror selfie, in which he wore a white tank top, aviator sunglasses and had a toothpick in his mouth, he wrote on Instagram: "Officially the longest I've gone since I was a teen without some kind of nicotine or marijuana in my system(among other things…).

"Feeling thankful for the freedom that comes with breaking addictions and dependency on substance.

"Sobriety, clarity, and spiritual connectedness feels real good.(sic)"

And the 'Shooter' star - who also has Kailani, 12, with former girlfriend Alexis Knapp - is determined to keep looking after himself.

He reposted the photo on his Instagram Story and wrote: "My only remaining addictions are toothpicks + self-improvement."

Reese is also mother to son Tennessee, 10, whom she has with ex-husband Jim Toth.