Final answer:
The chemical factor that is NOT involved in the skin's resistance to infection is 'Complement proteins,' as they are not produced by the skin but instead are part of the immune system found in the blood.
Step-by-step explanation:
The skin has several chemical factors that make it resistant to infection. An acidic pH prevents the growth of bacteria by creating an environment that inhibits their survival.
The enzyme lysozyme, present in saliva, mucus, and tears, breaks down bacterial cell walls, leading to the death of the bacteria. Sebum, produced by sebaceous glands in the skin, contains substances that inhibit microbial growth but also provides nutrients that some microbes can use, thus not directly acting as a barrier to infection. However, the complement proteins are not produced by the skin but rather are part of the immune system present in the blood, and they help in destroying pathogens through a cascade of reactions leading to the lysis of pathogens.
Therefore, the option that is NOT a chemical factor in the skin's resistance to infection is 'Complement proteins,' as it is not produced by the skin itself. These proteins are part of the immune system's defenses and circulate in the blood.