The much-maligned feral pigeon is often labelled a health risk, but those who maintain this conveniently forget that any bird or animal can carry diseases, but that doesn't mean they actually do. The other point is that almost no 'pigeon diseases' can be transmitted to people. The reality is that pigeons pose no greater health threat than any other bird or animal - wild or domestic - and, indeed, far less so than pets and our fellow-humans!
Real experts in the field all agree that there is no tangible health risk to human beings from contact with pigeons: People who know what they're talking about
Those whose occupation or leisure pursuit involves close contact with pigeons should, obviously, take sensible hygiene precautions as should one who deals with any animal, including household pets. That said, the risk of contracting disease from a pigeon is minute for the 'ordinary citizen'
Pigeon or other bird droppings in any quantity are, of course, unsightly. In the UK, the RSPB warns that these are a hazard if they contaminate food or grain stores - so for Joe Public, the answer is probably to not allow a pigeon to paddle in your cornflakes!
The most common bird-related problem does not, however, arise from a 'bird disease'. Many people will have heard of 'bird-keepers lung' or 'pigeon fanciers lung'. This is actually an allergic reaction (allergic alveolitis) to minute particles and dander from birds. It can be contracted by both pigeon-keepers and owners of pet birds such as parrots, cockatiels and budgerigars, through inhaling the dust in confined spaces. Many pigeon fanciers will wear a protective mask when cleaning the loft, but few pet owners are likely to even think of that in relation to birds living in the home. Some sensitive people have been known to develop the condition even from the residue left from a previous occupier's pet birds. A protective mask should also be worn if long-standing accumulations of dried droppings are to be cleared, to avoid inhaling powdery particles.
If a pigeon presence is a problem, there are usually ways of dealing with it which cause no harm to the birds, who simply want to eat, sleep, raise a family or pass the time of day in the only environment they know. Access to balconies can often be blocked by installing special sprung and tensioned wire above railings, and/or blocking any pigeon-sized gaps with mesh. Many roofs have mesh, or 'porcupine' wires (always install plastic ones!) along edges, as do large windowsills, or ledges and crevices in older buildings. Never use gels or other 'paint on' substances, as these simply cause the birds injury and mess up railings, etc. It's best to contact an organization like the RSPB, or PICAS for information, and have work carried out by a well~reputed and eco~friendly company.