Heme-containing oxidoreductase which catalyzes the conversion of thiocyanate (SCN(-)) into antimicrobial agent hypothiocyanous acid (OSCN(-)) in the presence of hydrogen peroxide (H2O2) (PubMed:6295491). Also involved in the conversion of iodide (I(-)) into hypoiodite (IO(-)) in the presence of H2O2 (By similarity). Responsible for the inactivation of a wide range of micro-organisms and hence, important component of defense mechanism (PubMed:12626341). Shows antibacterial properties against Pseudomonas aeruginosa (PubMed:12626341). The lactoperoxidase-SCN(-)-H2O2 system shows antibacterial properties against Burkholderia cepacia and Haemophilus influenzae in vitro (PubMed:12626341). Present in mammary and salivary gland secretions and may contribute to airway host defense against infection (PubMed:12626341). May contribute to maintaining an appropriate H2O2 cellular level, therefore protecting cells from H2O2-caused injuries and inflammation (By similarity). {ECO:0000250|UniProtKB:P80025, ECO:0000250|UniProtKB:Q5SW46, ECO:0000269|PubMed:12626341, ECO:0000269|PubMed:6295491}. This is the function of LPO (lactoperoxidase, ENSG00000167419).