kratzen
to scratch
To rub the skin with fingernails or a pointed object, often because it itches.
Der Mückenstich juckt so sehr, ich muss mich ständig kratzen.
The mosquito bite itches so much, I have to keep scratching myself.

to scratch
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to scratch
To rub the skin with fingernails or a pointed object, often because it itches.
Der Mückenstich juckt so sehr, ich muss mich ständig kratzen.
The mosquito bite itches so much, I have to keep scratching myself.

When you rub an itchy spot on yourself, 'kratzen' (to scratch) is often used reflexively: 'sich kratzen' (to scratch oneself). You can also add the body part as a direct object: 'sich den Arm kratzen' (to scratch one's arm).
Hör auf, dich ständig zu kratzen, du machst die Haut kaputt!
Stop scratching yourself all the time; you're damaging your skin!
To describe a rough feeling in the throat, 'kratzen' (to feel scratchy) is often used impersonally with 'es' (it) or with 'der Hals' (the throat) as the subject. The person feels the scratchiness but is not actively doing the scratching.
Es kratzt mir im Hals, ich sollte einen Tee trinken.
My throat feels scratchy; I should drink some tea.
In the figurative meaning 'Ansehen beschädigen' (to damage someone's reputation), 'kratzen' (to undermine) always appears with the preposition 'an' followed by the dative. You 'scratch at' someone's image or reputation.
Diese Affäre könnte empfindlich an seinem Ruf als zuverlässiger Partner kratzen.
This affair could seriously undermine his reputation as a reliable partner.
The colloquial expression 'Das kratzt mich nicht' means 'I don't care about that.' The person who does not care about something is always in the accusative.
Seine Meinung kratzt mich nicht im Geringsten.
His opinion doesn't bother me in the slightest.
The expression 'jemanden nicht kratzen' (to not bother someone) is clearly colloquial. In formal situations or in written language, you would use other expressions.
Was die anderen über mein Hobby denken, kratzt mich ehrlich gesagt nicht.
What others think about my hobby honestly doesn't bother me.
When 'kratzen' (to scratch) describes damage, the object is often a sensitive surface. Typical objects are paintwork, a CD, glasses, or furniture.
Pass auf, dass du mit deiner Tasche nicht die frisch gestrichene Wand kratzt.
Be careful not to scratch the freshly painted wall with your bag.
to interest
'interessieren' and 'jemanden nicht kratzen' are opposites in this meaning. 'interessieren' says that someone has attention or curiosity for something. 'Das kratzt mich nicht' is colloquial and means: it does not interest me, or I don't care. It can be confusing because 'kratzen' normally has a physical meaning and is used this way only in a fixed, informal expression. For neutral German, 'interessieren' is safer. 'Nicht kratzen' is more appropriate in conversations among friends or in very informal language.

Der Lärm von der Straße kratzt meine Nachbarin nicht.
The noise from the street doesn't bother my neighbor.
Du interessierst dich in der Pause sehr für die neue App.
During the break, you are very interested in the new app.