This is a great question, because the common initial signs of stress or anxiety are easily, and therefore often, overlooked!
Dogs communicate with their whole bodies, the way they behave, their voices, and also through deliberate use of scent – for example, they exude pheromones which, through smell, can tell other dogs lots of personal information, including how they’re feeling however, this remains beyond our human capability. Thankfully Dogs Trust have a helpful guide: https://www.dogstrust.org.uk/dogadvice/understanding-your-dog/body-language
Signs of stress or anxiety in your dog
Very obvious signs a dog is feeling uncomfortable about something that is happening, or might be about to happen, might include whining/barking and franticly trying to seek our attention, or get away from whatever it is that’s troubling them or behaving aggressively to try to make whatever’s troubling them go away instead. However, recognising the subtle signs of increasing discomfort means we can help dogs feel safe long before they become this upset.
Subtle signs of escalating stress/anxiety include muscles becoming tense, slowed movement, and lowering their body to the floor, as though attempting to appear smaller/less threatening. Ears are held back, tighter against heads, and with narrowed eyes to avoid staring intently, which could be intimidating to others. But you might also see the whites of eyes as they scan for potential danger. As facial muscles tighten, foreheads become furrowed – like many of these signs, difficult to detect in fluffier dogs. Watch for little repeated tongue flicks and lip-licks. Dogs might also yawn and pant when not at all tired, or hot.
Another giveaway sign are tails lowered and/or tucked right beneath tummies. Anxious dogs generally want to avoid whatever’s concerning them, so might move behind you, turn their heads, or lean away. They’ll want to keep aware of any danger so could become vigilant and agitated; however, are likely to keep their weight backwards, in the way you might lean back in your chair if a scary spider suddenly appeared crawling across your computer screen. They might also lift a paw to demonstrate zero desire to join in any activity. You might see their tail tip twitch very slightly, too.
Other signs might include trembling and pacing because their body is full of nervous energy. A dog might also jump up much more than usual and appear demanding something of you, they might also grab treats less gently than usual. You might also see a change in eating or sleeping patterns, as well as changes in usual behaviour – for example, not wanting to play or walk in a particular place any longer.
It’s important to consult your vet when you believe your dog to be stressed, because the reason might be medical, and your vet can either rule out any trouble brewing or treat nice and early! Your vet can also refer you to an accredited clinical animal behaviourist to help you get to the bottom of your dog’s stress/anxiety and help them feel and behave differently.