Many breeds of dog have been demonised for being aggressive towards people, but any dog is capable of being aggressive. There are several reasons for dogs to show aggression towards a person; therefore in order to treat the problem accordingly it is vital that the reasons behind the aggression are properly diagnosed. Prompt action is necessary in order to avoid human injury as well as legal action against the owner, and life-long restrictions on the dog or its destruction.The main motivations for a dog to display aggression towards a person are fear, defence of a valued resource, and pain. Every dog is capable of showing aggression but whether it does or not will depend on a number of factors including, genetic traits, previous learning experiences, the ability of the animal to communicate and the behaviour of the person. Fear is a very common motivation for aggression. Unfortunately, it is frequently misdiagnosed, often being labelled as dominance aggression instead. It may be misdiagnosed because of the appearance of the dog while showing aggression. A fear aggressive dog is typically considered to show classic signs of fear while showing aggression, for example they have a lowered body posture with the weight distributed towards the back legs, the ears are flattened against the head and the head and tail are lowered. However, the more a dog shows aggression and it works to make the object of its fear back away, the more likely it will choose this response again in the future. As the behaviour is perceived as being successful in increasing distance between the dog and the scary person it will become more confident in its use of the aggression, even though the reason for showing the aggression is still because it is scared. Thus the dog begins to show more confident body language during the aggressive display, for example it adopts a more upright posture with the weight shifting forwards, ready to lunge towards the person if necessary. The ears, head and tail can also be held higher. The tail may even be wagged in a narrow, stiff arc. Unfortunately, it is these dogs that are often labelled as being dominant-aggressive and can be punished as a result of trying to reduce the dog's status compared to the owner. However, with any dog, but particularly with dogs that are already in fear of the owner, or people in general, then punishing it will only make the fear worse, and potentially enhance its need to use aggression to protect itself. Fear aggression can develop through a lack of adequate exposure to people during the socialisation period or because of a negative experience later in life. Some dogs are also genetically predisposed to developing aggression and are more likely to choose this option over running away, hiding or freezing. Of course these other options are not always available and if the dog learns to use aggression because, for example they are cornered or on a lead and cannot run away they have no option to use aggression in order to defend themselves. They might then learn to use this option again in future and not waste time trying to hide or run away and risk being hurt. Therefore, some dogs who would perhaps prefer to run away or hide learn to use aggression as a first choice to deal with frightening experience, because of what they have learnt in the past. Well socialised dogs will also try to use appeasement behaviours to defuse a situation of conflict. If they are scared by the approach of or handling by a person, they will avert their eyes, lower their body and head, and drop their tail. If the person still continues to approach then the dog may tuck its tail between its legs where it may wag, lift a front paw, lick its lips and perhaps yawn. If the person still continues to approach the dog may roll over onto its back and may even urinate. If the person still continues to approach or handle the dog then feeling he has exhausted his appeasement options the dog may turn to aggression as a last option. The dog may then stare at the person, if this does not work to get rid of them then he may start to lip lift, growl or snap the air. Again if this does not work the dog may bite. Therefore, the behaviour of the person is very important. People must be very aware of what behaviour might frighten dogs. In general this will be approaching a dog directly from the front and leaning over a dog. But dogs will have individual likes and dislikes regarding their interactions with people. It is therefore imperative that people can also recognise the signs that a dog is not comfortable with their approach or handling. They must recognise appeasement signals. If they do not, they may end up getting bitten. The dog may also learn that there is no point in using appeasement signals again in the future and choose to use aggression earlier in similar situations in the future. Similarly, if a human ignores the early warning signals of aggression, such as staring and lip lifting, the dog may learn not to waste time showing these behaviours again in the future because they are not successful at getting the scary person to back away. They may then use an escalated display of aggression earlier in future situations where they feel threatened by a person. This is common in small dogs, which are commonly misdiagnosed as being impulsive if they do not show warning signals before biting. Whereas in reality they have just learnt that warning signals are ignored. Imagine being confronted by a snarling Yorkie and a snarling Doberman and you might understand why some dogs learn that warning signals work whereas others are taken more seriously! Owners may also ask their vet to neuter male dogs that are being aggressive. However, if the motivation is fear then castration can actually increase the aggression as what little confidence the dog had has been removed by the reduction of testosterone. Unfortunately, many vets may not realise this and encourage owners to have their dogs castrated if showing aggression. Many of these dogs are only referred to a behaviourist after the castration, and after the aggression has worsened. This illustrates how important it is to receive an accurate diagnosis for the aggression before attempting any treatment.Although this is the most common form of aggression displayed towards humans, other types of aggression must also be considered, for example resource guarding, pain-related aggression, and maternal aggression. These all require different types of treatment and as aggression is such a severe behaviour problem in terms of the state of wellbeing it reflects in the dog as well as being an important public health and safety issue it is vital that an accurate diagnosis is made and appropriate treatment followed.