The white pus that squeezes out of a nail groove is pus, mostly caused by Staphylococcus aureus infections.
Onychomycosis is an abscess in the nail groove and surrounding tissues that forms yellow and white pus when bacteria, necrotic pus cells, and some necrotic and detached tissue mix. Since abscesses caused by Staphylococcus aureus do not spread, they usually form under the skin and become localized and raised. Most patients will experience redness, swelling and pain. If there is a white substance, it may be pus coming out.
Onychomycosis usually begins without an abscess, but if the condition worsens, it can become pus-filled and an abscess can form around the nail. At this point, if the abscess is not cut and drained in time, the abscess may spread under the nail and yellow and white pus can be seen under the nail.
When white pus is squeezed from a nail infection, it is recommended that medical attention should be sought promptly to prevent the condition from worsening.