The most common negative items
Late payments (30, 60, 90, 120+ days), collection accounts, charge-offs, repossessions, foreclosures, debt settlements, tax liens, judgments and bankruptcies. Hard inquiries are technically not negative, but too many in a short window can still cost you points.
Each item carries a different weight. A single 30-day late payment on a recent account can hurt more than an old collection, because scoring models care heavily about how recent the damage is.
How long they stay
Most negative information stays on your report for seven years from the date of first delinquency. Chapter 7 bankruptcy stays for ten years. Hard inquiries drop off after two years and stop affecting your score much sooner than that.
Time alone does not fix a report that is wrong. An item reported with the wrong date can sit on your file years longer than the law allows.
What can actually be challenged
Accurate, timely and verifiable information cannot be removed from a credit report. What can be challenged is information that is wrong, outdated, duplicated, or that the furnisher cannot verify when asked.
In practice that means wrong balances, wrong dates, accounts that were never yours, debts included in a bankruptcy still reported as owed, duplicate collections for the same debt, and paid accounts still showing a balance.