If it stop the water to reach then it is not allowed
It is permissible to have a tattoo if:
a. The tattoo allows the water of wudhu and ghusl to reach the skin while performing wudhu or ghusl.
b. Having a tattoo does not involve forbidden touch or look.
c. The tattoo does not encourage corruption or corrupted ideas or beliefs.
d. The tattoo does not have the names of Allah his almighty or Quran script.
e. for woman, if that is considered as a beauty item then it must be concealed from non-mehram man