After tissue damage, there is accumulation of hydrogen ions. These protons may activate nociceptors via acid sensing ion channels - a family of sodium channels on cell membranes that have a role in pain transmission.
Of special interest is one type found only in small dorsal root ganglion neurons that are responsible for activation of nociceptors.
Suzuki R, Sikandar S, Dickenson AH. Nociception: basic principles. In: Bruera ED, Portenoy RK (eds) Cancer Pain Assessment and Management. Cambridge University Press . Cambridge 2010, P 6.