"We are deeply saddened by Hayden Panettiere's passing," the company said in a statement shared on Instagram on Thursday. "For more than a decade, Hayden was a valued member of our Neutrogena community. We are proud to have partnered with her and understand that we made her feel unsupported during a very difficult time."
It added, "This is not what Neutrogena stands for or who we want to be."
Panettiere, who died Sunday at age 36, wrote about her decade-long partnership with the brand in her memoir, "This Is Me: A Reckoning," which was released in May this year, speaking further about the business relationship and Neutrogena's 2016 decision not to renew her contract in several interviews at the time.
In its social media post Thursday, Neutrogena indicated it would be investing in resources to aide women experiencing postpartum depression, in the wake of Panettiere's death.
"Hayden's courage in sharing her challenges helped inspire important conversations and awareness," the company wrote. "We are making a significant investment to a long-standing community health partner to help give more women access to the support they need, including care for postpartum depression."
The company said it would share more details about the investment at a future date.
"Out of respect for Hayden's family and loved ones, we did not want to speak out so soon following her passing. Everyone at Neutrogena extends their deepest condolences to Hayden's family and all who loved her," it added.
Panettiere previously opened up about her experience with postpartum depression in an interview on "Live! With Kelly and Michael" in 2015.
She broached the subject while discussing her character Juliette Barnes from the ABC and CMT series "Nashville," who also experiences postpartum depression in season 3.
In the interview, Panettiere called postpartum depression "something that I can very much relate to."
"You don't realize what broad of a spectrum you can really experience that on," she said at the time, noting that the condition is one "a lot of women experience."
"It's something, I think, that needs to be talked about," she added, "and women need to know that they're not alone, and that it does, you know, heal."
Postpartum depression is a serious mood disorder that can occur within the first 12 months after childbirth. It affects as many as 1 in 8 women, according to the Centers for Disease Control and Prevention, and can cause symptoms including withdrawal from loved ones, excessive crying, anxiety, anger, self-doubt and intrusive thoughts.
The condition is more intense that the so-called "baby blues," can last for weeks or months, and usually requires medical treatment.
Panettiere also spoke in her 2015 interview about the need to support women struggling with postpartum depression.
"There's a lot of people out there who think that it's not real, that it's not true, that it's something that's made up in their minds, and 'Oh, it's hormones,' and they kind of brush it off," the actress said at the time. "It's something that's completely uncontrollable, and it's really painful, and it's really scary -- and, you know, women need a lot of support."
In May this year, more than a decade after her "Live! With Kelly and Michael" interview, Panettiere sat down with the "Jay Shetty Podcast," saying her 2015 comments allegedly led to the end of her decade-long ambassador partnership with Neutrogena.
"I had no intention of, or plan to, talk about postpartum depression. It just came up, and I was just being honest," she said on the podcast, referring to her 2015 interview. "Never for a second did I think that anyone ... cared, that anyone would have a bad reaction to it. It was my truth."
She then stated that she "got that call that Neutrogena wanted to fire me over that, and my representative at the time said, 'That's illegal. You can't do that.'"
According to Panettiere, her representative "saved the day that year," but the actress "knew that that was going to be it, that ... I was not going to be invited back the next year."
Panettiere's comments on the scuttled Neutrogena partnership resurfaced this week in the wake of her death, with fans and supporters flooding social media to criticize the company, some of them urging a boycott.
ABC News has reached out to Neutrogena for comment.
If you or someone you know is struggling with thoughts of suicide -- free, confidential help is available 24 hours a day, 7 days a week. Call or text the national lifeline at 988.