Cockroach populations that have established themselves within human-built structures are considered pests for many reasons; disease transmission, odours, contamination, allergic reactions and even biting…

• Disease Transmission:
  Cockroaches may carry and transmit diseases of humans, as they like to frequent areas like grease-traps, drains and sewers where disease organisms are easily picked up or ingested. Each cockroach may carry several million bacteria on and inside their bodies.
• Contamination:
  Food, food utensils, food product storage areas (pantry), and virtually any surface that they contact or where they congregate will be fouled by  their droppings, discarded skins (cuticle), empty or full egg cases (ootheca), dead cockroaches and vomit.
• Odours:
  Large populations of cockroaches may have a strong, recognisable and unpleasant odour, due to secretions from their mouths and cuticles (and droppings).
• Allergic Reactions:
  Many people are known to be allergic to cockroaches, exhibiting skin reactions and/or asthmatic type reactions. The allergen can be ingested where food is contaminated, or inhaled when faeces and discarded skins dry out and become part of your air-bourne household dust.
• Fear and/or Bites:
  Many people find the presence of cockroaches unbearable and/or frightening, perhaps due to their appearance or because of their quick and unpredictable movements. Although rare there have been reports of cockroaches biting people (fingernails, toenails and callouses).