In high school, people called Dani Pearsall "the dragon lady". Her ambition and drive meant many saw her as stern and rude, and kids often expressed "mild disgust" if partnered with her in class. By the time she got to college, people in her creative writing class were begging to work with her. "People were like, 'Wow, you’re so cool, you’re so honest,'" the now 25-year-old store manager says.

Jud Nichols, a 31-year-old public defender from Minnesota, played basketball with the same group of guys for many years. Initially, he never received any praise from his teammates. "I’m a very average basketball player," he laughs, "but suddenly people would be like, 'Dude, you played really well. Good game.'"

Dani's personality hadn’t changed – and neither had Jud’s basketball skills. What did change, undeniably, was their appearances.

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In 1920, the American psychologist Edward Thorndike coined a new term. The "Halo Effect" is a cognitive bias which means that when we see one good trait in a person, we overestimate their other positive traits (the first trait is like a halo, shining light on an individual). In 1972, three psychologists demonstrated the effect by asking volunteers to rate people’s personality based on photographs alone. Overwhelmingly, participants assumed more attractive people were also more kind, trustworthy and successful. The paper was titled "What is beautiful is good".

This might not shock you. Many believe in "pretty privilege" – the idea that beautiful people have an easier life. Yet the halo effect is sometimes called the "horns and halo effect" – because it has a flip side. When someone is unattractive, people may assume they have bad qualities. But just how pervasive is this phenomenon? Just how damaging?

Five people whose appearances have changed dramatically agreed to speak with me for this piece. Each individual has gone from conventionally unattractive to conventionally attractive in Western society’s eyes. Thin bodies are valued in the West and studies have shown obese people face social stigma, so this article includes some people who have lost a significant amount of weight – though these individuals also changed other grooming habits to fit society’s idea of an "attractive" person.

Emma, before and after

"If I would’ve stayed bigger and not lost any weight, I wouldn’t have known that how I was being treated before was really any different," says Emma Passe, a 34-year-old account executive. "Now, I completely see a huge difference."

Overweight most of her adult life, Emma decided to lose weight aged 31 when she started struggling with sleep apnea, heart palpitations and body acne. "The more weight I lost, the smaller I became, more people wanted to talk to me," she says. She tells me people are kinder than she used to think – sticking around to chat more, saying hello when they usually wouldn’t, asking about her day. "I thought everybody was just regularly friendly, but now everyone is super friendly."

The fact people are friendly hit Ashley (who doesn’t wish to give her surname) the hardest. The 30-year-old from Portland tells me, over email: "Now, when I make eye contact, people’s faces light up and they smile at me!" Her shock is evident in an abundance of punctuation ("Wow, people smile???") as she describes other revelations. People go out of their way to help when she asks, and strangers strike up conversations. "People listen to me… I actually feel like a member of society."

Ashley, before and after

Like Emma, Ashley realised these things after losing weight. Bullied as a child, she says she felt like "hot garbage" before she met her husband and lost 165lbs, learnt about make-up and skincare, and altered her fashion sense. Although she predominantly feels "relieved" that people are now friendlier, there is some bitterness. At her heaviest, Ashley says people taunted her and others treated her with pity and disgust.

"I think a pile of shit would probably get less disdain than I did," she says. "When you see the duality in people so clearly it makes it difficult to like anyone new. They might be nice now, but would they have been nice when you were double your weight?"

"If you want something, you smile and you get it – it's really crazy."

Dani pauses for a long time when I ask if there are any downsides to her transformation. In high school she dressed in unisex clothing and avoided make-up, meaning she was often called "sir" by strangers. In college, she started wearing dresses, grew her hair and learnt how to contour via YouTube tutorials. "Umm," she answers eventually. "Honestly, it’s pretty awesome. It has lots of advantages."

Unsurprisingly, Dani – like many of my interviewees – started getting more attention from the opposite sex. "I was still Dani and I hadn’t changed, but suddenly half of the population had woken up to the fact that I existed." As well as an improved sex life, she also found that interactions with male and female customer service workers became easier. "If you want something, you smile and you get it – it's really crazy." She puts on a vocal fry, exaggerating a feminine whine: "Hiiii, I’m sorry but I can’t find this book. Could you, like, look in the back for me?" She says it works.

"It's crazy. It's crazy. You know what, I don't know how people who are pretty their whole lives aren’t just total egomaniacs, because it's just so easy to get what you want."

Kameron, before and after

Attention from the opposite sex is the most obvious outcome of an "improved" physical appearance, but Kameron Rytlewski, a 23-year-old from Michigan, thinks his increased confidence may also have played a part. "My weight was holding me back from being the person I really wanted to be, or at least the person I envisioned being," he says.

People used to ignore him or treat him with a "general negative disposition", but now they are far friendlier. "Comments and attention from the opposite sex have definitely been more positive. Friends and family still pretty much treated me the same."

If the fact the opposite sex treat you better when you become conventionally attractive isn’t shocking, the fact family members do probably is. Dani says her dad criticised her appearance growing up, often telling her to wear make-up. When she got older and used make-up, "he was definitely a lot more supportive of my life". Jud, the man who was complimented more at basketball after he lost weight and started taking advice from male grooming books, says family also treated him better. "Even the people closest to you tend to treat you a little bit differently," he says, explaining that family members were friendlier and wanted to chat more often.

Jud, before and after

Like Kameron, Jud wants to add the disclaimer that how he felt about himself potentially impacted how others treated him (this is something both of the men interviewed said, but none of the three women). With that disclaimer aside, however, he says people are now far more receptive to his jokes.

"My humour is kinda deadpan and sarcastic… When I looked less healthy, I think people were less inclined to understand that I was totally kidding, whereas now it seems more like they get it."

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Out of everyone I interviewed, Emma seems to have experienced the most drawbacks from changing. "The biggest thing for me, the biggest surprise, is that I have lost friends," she says, explaining that overweight friends cut her off.

Emma describes another "nightmare" of losing weight. Although she is married, men hit on her often, which is especially frustrating at work. "I am always being asked for coffee or lunch or being told I'm pretty or beautiful," she says. "It feels pretty awful to feel like you're constantly being hit on, or someone is really only talking to you for that purpose and not to get to know you... it's really disheartening." These experiences show there are downsides to being conventionally attractive, and that lookism works in many ways.