Do we inherit loneliness from our parents in the same way we inherit our hair and eye colour? Two women explain how loneliness has played a part in their lives - and how it relates to their parents and children.
"Loneliness for me is constant. No matter where I am, it just doesn't go away. It's almost like you can feel it in your bones, this deep feeling of wanting to fit in and wanting to be around people you know and love, but you can't.
"I do think I have inherited it. It's kind of been passed on to me."
Angel Kissi and her mum Hayley, both struggle with anxiety, depression and loneliness. For her mum, the latter was sparked by severe post-natal depression. For Angel, it started when she was a child.
"My family stood out in Peterborough. Everyone knew who we were because we looked different. I'm really tall and mixed race and I stood out," says the 20-year-old. "When I went to university, things were good but I still felt like I didn't fit in. I thought moving to London would change that and it didn't.
"I still felt like I was quiet and awkward. I really struggled to connect with people and make friends straight away. Everyone was going out for drinks after class and I was never invited. I felt like I was doing something wrong.
"Eventually I stopped going to my lectures. I would get up, get ready to go and then go back to bed. I would avoid going to shared areas of my flat, I shut myself away and isolated myself. I went into the loneliness and let it take over."
Unable to cope, Angel left university before the first year was over. Although she felt a strong desire to go home and be close to her mum, she rented a room close-by.
"It's good we don't live together because we would be bringing each other up and down all the time. She has definitely helped me with some aspects [of my mental health] but other times I didn't want to speak to her because I didn't want to make her worse.
"If she was different, then maybe I'd be different. I don't blame her at all, she didn't choose to be like this, it's not her fault. It's probably something that I have got from her. Personality traits or attitudes that I've learnt from her without meaning to."
According to Age UK, loneliness is defined as feeling a lack of affection, closeness or social interaction with others.
The charity Mind says it is not a mental health issue but research suggests it is associated with an increased risk of depression, anxiety, low self-esteem and stress, and can be triggered by major life events such as bereavement, relationship break-ups, retirement, changing jobs and moving.
Dr Rebecca Nowland, who has researched the subject of loneliness, says it can be passed down in families.
"I don't think we're going to find a gene for loneliness but it's about how we respond to an experience of loneliness that might be genetic," she said.
"There has been a number of studies that have indicated that loneliness is certainly hereditary, that it might run in families and there might be associations between a parent's loneliness and a child's loneliness.
"Being parented by someone who has been in a lonely state for some time means we might transmit some of those negative feelings. It's the transmission of negativity that might be happening rather than the experience of loneliness itself."
Kirsty McGrath thinks loneliness became a problem for her after her son was born five years ago. She tried going to a number of mother and baby groups to make new friends but struggled to organise play dates and found herself increasingly isolated.
Although her husband supports her in the evenings, she finds daytimes difficult because she is often alone and has no-one to talk to. The 33-year-old teacher, who lives in Eltham, south London, says she is worried that not being able to socialise her children will have an effect on them and she might pass on her own feelings of loneliness, which she describes as a "grey cloud".
"I am paranoid of passing it on to the kids, I wouldn't be surprised if I did. It's something I am very aware of. I just want them to feel comfortable around others and not feel like they don't fit in.
"My son has come home from school and said to me that he doesn't have any friends and that he hasn't played with anyone. I'm worried he is like this because of me, that I haven't put him in enough social situations to know how to mix with others."
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Loneliness is a common experience among new parents and finding groups with shared interests, as opposed to those just focused on parenting, is one way to cope, says Dr Nowland.
Dr Faruq Fazal, a GP who has worked in mental health services, says loneliness comes about when people don't have a support network and believes teaching coping skills in school could help.
"Nobody really teaches you how to cope through life's challenges. For those suffering from loneliness, it's not just about physically having people around you, it's when you feel you're not able to talk to people and you don't have any emotional support," he says.
"I see people who don't have a support network and their coping strategy has gone."
Mind suggests a number of ways to manage loneliness, including peer support and talking therapies.
Dr Nowland says seeking professional advice can also help those stuck in a cycle of behaviour brought about by loneliness.
"Loneliness leaves you with this emotional feeling that is quite painful and distressing. If someone is lonely and they have felt it for a long time, it's realising that it's ok and that you might have developed negative thought patterns.
"You might need some help with cognitive behaviour therapy to help you think and reframe things."
Angel has had counselling but says although it has helped with her anxiety, it hasn't helped with her feelings of loneliness.
She returned to university briefly but has since decided to focus on her mental health, work, and learning to drive.
"Loneliness is really different from anxiety and it's different from not being able to make friends," she says.
"Anxiety can isolate you, but the loneliness that I felt at university was separate from that - it's about being around people, but being in your own little world.
"I'm in a relationship and I'm close to my family but that loneliness is still there. Overall, things have improved a lot, but I don't know if it's ever going to go."