Research has shown that the pandemic exacerbated teen mental health issues, as the lockdown severed connections between young people at the most critical developmental stages. According to the Substance Abuse and Mental Health Services Administration (SAMHSA), nearly 20% of those aged 12 to 17 had a major depressive episode in 2022. The percentage of high school students reporting feelings of sadness and depression has increased since the onset of the pandemic, although adolescent mental health was already steadily declining, per the CDC.

This week, a new study found the pandemic may also have changed the teenage brain structurally—most dramatically affecting teen girls as compared to teen boys.

The study published in the Proceedings of the National Academy of Sciences journal Monday found that teen girls’ brains aged 4.2 years faster than they normally would and teen boys’ brains aged 1.4 years faster than they normally would during the COVID-19 lockdown.

Researchers tested the thickness of teens’ brains’ outer layer or cerebral cortex before and after the COVID-19 lockdown. The brains of teen girls experienced accelerated aging across 30 regions, all a part of social-emotional processing, compared to two regions in teen boys, ones involved in visual processing.

The authors hypothesize that stress played a role in the brain’s accelerated aging—and that teen girls, who are more apt to socialize emotionally with peers, experienced the structural brain changes of the lockdown more dramatically.

So, if COVID-19 structurally changed the teenage brain, what does that mean for teens now? And is it possible to reverse the effects?

To answer these questions, Fortune spoke with Dr. Elizabeth Ortiz-Schwartz, a child psychiatrist based in Connecticut and a Distinguished Fellow of the American Psychiatric Association.

Fortune: This study found that the teenage brain aged more than it normally would during the pandemic. Why do you suspect this happened?

Ortiz-Schwartz: The teenage brain maturation with exposure to trauma or serious conditions like neglect or war has been very well documented. This is a study that was checking on teenage brains and looking at the MRIs, and then it just so happened that the pandemic hit, and they continued to do the MRIs. It’s a clear indication that there’s maturation, but not in a positive way. It’s not that the brains are getting smarter or brighter, but it’s that the cortex is getting thinner and thinner in areas that vary by gender. It means that the brain is being exposed to stress hormones at a significant level.

Fortune: How does stress and adversity affect the aging of the teen brain and why may it vary by gender?

Ortiz-Schwartz: The [teen] brain is already undergoing a lot of dramatic development. When you have a brain that’s so open to change, and you have adverse conditions, the brain will develop differently. In this case, it has accelerated the things needed for survival under stressful situations. And, it’s at the expense of some of the aspects of development that you would like to see in a more nurturing environment. It’s putting the brains under duress.

Female brains are known to be more wired to react socially to different signals and to be more social, but they also tend to have higher levels of anxiety and depression. Having females deal with less social interaction and how that was so limited is significant. (The authors note that accelerated aging of the teen brain due to adversity can increase young people’s risk of behavioral and mental health issues)

Fortune: Is accelerated brain aging due to stress always entirely a negative thing?

Ortiz-Schwartz: Cortical maturation may not always necessarily be a negative thing. It’s an adaptive thing. When a person is in a stressful environment, the brain is set up to function at a higher level in the areas that have to do with avoiding dangers and fears— like the amygdala, which makes you more alert. So in wars, famines, and things of that nature, it is expected that the brain will have more energy towards those areas, but then there will be less energy for things that have to do with focus and attention and more positive aspects.

I don’t feel that there are tons of benefits for children to be of that maturity, especially if it’s associated with depression and anxiety. We’re not talking about emotional maturity. We’re talking about brains under stress.

Fortune: How is building resiliency an antidote to the accelerated aging teen brain?

Ortiz-Schwartz: The things that help to build resilience also help with depression and anxiety, and they also help to tone down the amygdala, the part of the brain that’s on activation that leads to the fight, flight, and freeze response that we see in trauma situations. The same things that help create resilience, including things like meditation, are some of the same things that we know help with chronic stress.

Fortune: What are other concrete steps to address accelerated brian aging in teens? What can be done to reverse this trend and not worsen it?

Ortiz-Schwartz: Our teenagers, especially our younger teenagers, need to feel that they are safe in the world. Post-pandemic, we need to continue to do the best that we can to create environments where [teens] feel supported, and that includes things like targeting and addressing bullying, targeting and understanding the effects of social media for especially the younger kids, and trying to put mental health support in schools. Families need a lot of interventions and support so that they can optimize their children’s mental health so that they can be supported. This is building resiliency.

From a clinical perspective, we know that teaching individuals to persevere and persist and not become avoidant and to learn really good skills to re-regulate and re-center can be healing. It’s about turning these negative experiences into learning and growth. It’s not about people feeling that individuals are broken or that people need to throw their hands up.

Many stress reduction strategies include managing sleep, appropriately decreasing the amount of overconsumption of social media, and being mindful about electronics.

Fortune: So, it’s not too late?

Ortiz-Schwartz: The hope is that the brains are plastic, and they’re going to be able to get back to a little bit more of a baseline. What I would love to see is having these kids be reassessed when they’re in their mid-20s to see if these changes continue or if there are positive factors that are introduced that manage that maturation.

The message for me, or my hope, is that we move forward with a better understanding that it is possible to reduce the chronic effects of the negative things that have happened. To do that, we need to be extremely mindful of what are some of the things that are going to contribute to good mental health, including managing sleep, which is something kids are struggling significantly with.

Now that there’s been a collective injury, we need to be much more mindful and proactive in how these things are instituted and help people live healthier lives and avoid more toxic stress to the brain.

Fortune: Is there a question a parent, guardian, or teacher can ask their teen to help them build resilience?

Ortiz-Schwartz: How is your stress level? How are you doing emotionally? That would be a really good question for parents and teachers to check in periodically. You get to learn a lot from the kids if you can have an opener like that.

For more on teens and mental health:

Is teen social media use a crisis or moral panic?
4 smartphone rules parents should follow, according to a social psychologist who has studied the Gen Z mental health crisis
10 essential tips for parents to raise successful, confident kids
‘I can’t just be on the sidelines’: Gen Z founders raised over $2 million to grow music therapy platform and tackle the youth mental health crisis

COVID rapidly aged our teens’ brains. Here’s how we fix them