People can look at themselves in the mirror and see an ugly, skinny skeleton when in reality they are muscular and buff. Then they would proceed to lift weights in self-hatred.
Someone could see a massive fat blob in the mirror when in reality, they are really hot, or really skinny, or really..not fat.
BDD is different for everyone.
"Preoccupation" doesn't cut it. You're anxious about your appearance at all times. When getting changed, when walking down the street, when looking at photos, when seeing an attractive person, whenever someone is looking your way, and whenever and surface with reflection catches your eye. Mirrors, windows, metal, water, anything. Obsessive thoughts invade your mind at any given opportunity. Concentration is on a task for about two minutes before thoughts stray back to listing all the reasons why you should loathe yourself.
The nature of BDD is delusional itself, meaning it’s difficult to separate reality from the falsehoods your brain makes you believe.
The reflection one sees in the mirror is different from what other people see.
The people you notice in public who stare and laugh at you actually are not.
3. Individual Characteristics
BDD causes one to obsess over specific body parts. For example, a bodybuilder with BDD could constantly stare at his arms and think 'oh god, they are so fucking skinny. Where is the muscle I work so hard for?? I need to lift heavier weights."
The thoughts about his biceps could manifest his brain all day, every day.
4. Extreme Desire to Change Appearance
Whether it's by working out, starving, eating, cosmetic surgery, or makeup, someone with BDD will have the incessant desire to change their 'flaws.'
The thought of "self-correction" is greatly appealing, but the problems that actually need fixing reside in a place much deeper than love handles and ears that stick out.
BDD is not vanity. It is quite the opposite. And it leads to depression, anxiety, and eating disorders in many cases.
The constant worrying about your appearance and hatred for yourself is clearly not helping one's mental stability. Being petrified if your thighs touch or if you're slightly bloated every single day, all day, is the building block for more serious mental illnesses.
Luckily, society is becoming more open to mental illness, despite the few who aren't, and I hope that those suffering from BDD receive help.