Boil

You cause one creature's blood to boil inside of them. The target must make a Constitution saving throw against your spell save DC. If the target succeeds, nothing happens. If the target fails, they take 1d6 necrotic damage immediately, and then takes 1d4 necrotic at the beginning of each of their turns for 1 minute. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage (both initial and later) increases by 1d4 for each slot level above 2nd.