"Asked him. Saw his scar. It's really there - like lightning."
-- Fred Weasley to his mother (PS6)
Harry Potter had several scars caused by various dangerous situations.
Harry was most famous for his famous lightning-shaped scar that he received when his parents were killed by Voldemort and he became the "Boy Who Lived." The scar became more and more painful as he grew older, and he realized it gave him a window into Voldemort's mind and experiences (GF2). Although Harry was never a true Horcrux created with Dark spells, his forehead scar held an accidental "soul-bit" that escaped from Voldemort's shattered soul when the killing curse rebounded due to protection of his mother Lily, who sacrificed herself to save him (PS1).
During several detentions in fifth year, Umbridge's black quill burned the words "I must not tell lies" into his hand (OP13). Even though Harry soaked it in a murtlap solution several times, the scar was still on his hand several years later.
While battling the snake Nagini at Bathilda Bagshot's house in Godric's Hollow, Harry received two more scars before Hermione rescued him: one from a snake bite on his forearm, and one from the Horcrux locket of Salazar Slytherin which left a "scarlet oval over his heart where the locket had burned him" (DH16, DH17). Hermione used dittany on his arm, but the locket scar lingered.
Harry had several other wounds that could have left scars, but either healed quickly or were cured by phoenix tears:
- In second year, Harry broke his arm in a Quidditch Match from a rogue bludger, and when Gilderoy Lockhart tried to fix it, he removed Harry's arm bones instead. He had to take Skelegrow in the Hospital Wing to put them back, but his arm never seemed the worse for wear (CS10, CS11).
- Also in second year, Harry was bitten by the Basilisk in the Chamber of Secrets and would have died if Fawkes the Phoenix hadn't come to shed tears on the wound, which then disappeared.
- In third year, Harry fell fifty feet from his broomstick when the Dementors came towards him. He recovered quickly but his Nimbus 2000 broomstick was smashed by the Whomping Willow (PA9)
- In fourth year, Harry was bitten by an Acromantula in the maze during the Third Task of the Triwizard Tournament. He was then kidnapped by Voldemort and cut on the arm by Peter Pettigrew. Fawkes later cured the Acromantula bite on his leg by weeping "thick, pearly tears" and mending the skin (GF36). The cut on his arm apparently healed the regular way and there was no scar.