Fear and Aggression

Fear is a protective emotion prompting the dog to either flight or fight the danger. Dogs can become afraid of an item they have not previously had any negative association to. During young dogs development, they will go through two distinct fear periods from between birth to 18 months. Between 8 and 12 weeks they can go through the ‘impact fear’ period, this is when they are learning to make sense of the world around them and distinguishing between safety and danger. The next is the ‘adolescent fear’ period also known as ‘the fear of situations’ period, at 6 to 14 months, often occurring during sexual maturity.
These fear phases are temporary unless handled incorrectly. Positive reinforcement is an essential tool to change the negative emotion to a positive experience, using praise or reward when the dog is scared. In addition to positive reinforcement, you must also remain calm and cheerful to demonstrate ‘there is no danger’.

your puppy is not fighting for survival in the wild. But her experiences—both positive and negative—stick with her for life. (Geier, 2021)
Fear in dogs can be easily mistaken for aggression, but never forget a scared dog can attack. Identifying the difference comes mainly from body language, a scared dog will hold their head down ears back, posture lowered accompanied by growling and snarling. It is extremely easy to identify a dog growling in fear from a dog who is warning you of an attack, they will appear much more confident body forward chest out. Any dog no matter how loving can attack if in a state of fear, wherever possible remove the dog from the situation causing the anxiety, if the growling is left to continue, they can go over their threshold and attack as they feel the need to defend themselves.
For example, this is the same way with people, if you are having an argument and getting more and more worked up, you start to shout at the other person, and you should walk away before losing it and throwing a punch, as you have gone over your threshold of being able to control how you feel.

Consider diet

Too much protein in a dog’s diet can affect Tryptohan levels, which is an amino acid used as part of the process to produce serotonin. Serotonin controls the dog’s mood, if the dog does not have enough Serotonin, they can become depressed, restless, anxious, and aggressive. Aggression goes hand in hand with anxiety, an outburst of aggression in dogs is a reactivity to how they are feeling.