How does stress 'cause' pimples?

Yes, I do have a huge fucking pimple on my forehead.
Stress doesn't directly cause acne, but it can worsen existing acne [1]. Studies have shown that wounds, including acne, heal more slowly when a person is under stress [1]. This is because when a person is stressed out, certain hormones are released and that process can lead to acne breakouts [3]. Stress pimples commonly appear around the jawline, chin, and cheeks [3]. The best way to avoid these breakouts is to manage your stress [3]. Getting a full 7 to 8 hours of sleep can also help [3].
The relationship between stress and acne has been misunderstood by many. Studies have shown that if you already have acne, stress does make it worse [1]. Researchers have found that wounds, including acne, are much slower in healing when a person is under stress [1,2]. Slower healing of acne means that the pimples stay longer and are more susceptible to increasing in severity [1,2]. It can also mean that more acne is visible at one time because it takes longer for each pimple to heal during a breakout [1]. Stress causes an overproduction of oil in your skin glands and spikes in adrenaline [2]. When your body faces spikes in certain hormones, especially those secreted from the adrenal glands, it strips moisture from the skin to prevent dehydration in other systems of the body [3]. To reduce moisture loss, the skin then produces higher levels of sebum oil [2]. Stress also interferes with a proper skin barrier function [3]. 