Phobic level responses to injections cause sufferers to avoid inoculations, blood tests, and in the more severe cases, all medical care.

It is estimated that at least 10% of American adults experience some level of fear of needles, and it is likely that the actual number is larger, as the most severe cases are never documented due to the tendency of the sufferer to avoid all medical treatment.

[1][5] Other medical journal articles have discussed additional aspects of this possible link between vasovagal syncope and evolutionary fitness in blood-injection-injury phobias.

[6] An evolutionary psychology theory that explains the association to vasovagal syncope is that some forms of fainting are non-verbal signals that developed in response to increased inter-group aggression during the paleolithic.

The physiological changes associated with this type of phobia also include feeling faint, sweating, dizziness, nausea, pallor, tinnitus, panic attacks, and initially high blood pressure and heart rate followed by a plunge in both at the moment of injection.

In recent years, a technique known as "applied tension" has become increasingly accepted as an often effective means for maintaining blood pressure to avoid the unpleasant, and sometimes dangerous, aspects of the vasovagal reaction.

This form of fear of needles causes symptoms that are primarily psychological in nature, such as extreme unexplained anxiety, insomnia, preoccupation with the coming procedure, and panic attacks.

It typically stems from repressive upbringing[citation needed] or poor handling of prior needle procedures (for example, forced physical or emotional restraint).

The suggested treatment is psychotherapy, this may include teaching the patient self-injection techniques or finding a trusted health care provider.

The symptoms include extreme explained anxiety,[clarification needed] and elevated blood pressure and heart rate at the immediate point of needle penetration or seconds before.

Some of these are blood, injuries, the sight of the needle physically or on a screen, paper pins, syringes, examination rooms, white lab coats, dentists, nurses, the antiseptic smell associated with offices and hospitals, the sight of a person who physically resembles the patient's regular health care provider, or even reading about the fear.