Yes it does, according to medical studies, but the reasons for it are probably behavioural and not physiological.
The AIBA's decision came as a result of scientific studies that showed that the number of concussions on matches with headguards is higher. A Vice article that talks about the International Olympic Committee's decision to allow boxers to not use protective headgear in the Rio olympics sums the issue pretty well:
Yesterday in Lausanne, Switzerland, the International Olympic Committee executive board declared that the IOC would not stand in the way of a 2013 AIBA decision to remove headgear from amateur boxing and therefore boxers at this summer’s Olympic Games in Rio de Janeiro, Brazil, will not be wearing headgear.
Their reasoning was simple and decent and rational and measured and based on research and statistics [...] "AIBA provided medical and technical data that showed the number of concussions is lower without headgear," IOC spokesman Mark Adams said yesterday. "They have done a lot of research in the last three years. The rule will go ahead for Rio."
The data Adams spoke of came primarily from two studies published in 2013 by the AIBA and the British Journal of Sports Medicine, both of which found that headgear not only doesn’t decrease the chance of concussions and lasting brain trauma in fighters; it increases it.
In the AIBA study, Charles Butler, the chairman of the association’s medical commission, studied 15,000 boxers, half of whom had competed with headgear and half of whom had competed without. He found that in the 7,352 rounds that took place with boxers wearing headgear, the rate of concussion was 0.38 per cent, compared with 0.17 per cent in the 7,545 rounds without headgear. The study found that headgear’s protective padding can cause extra jarring to fighters’ heads, give them a false sense of security, and make it more difficult to see punches coming, all of which can lead to brain damage.
"There's no evidence protective gear shows a reduction in incidence of concussion," Butler said. [...]
Butler’s research was backed up by a concurrent study conducted by the British Journal of Medicine, whose research determined that there was “no good evidence that mouthguards and helmets ward off concussion.” While researchers agreed that such precautions could help prevent often-serious facial cuts and head injuries (the introduction of headgear at the 1984 Olympics reduced both the number of lacerations and the number of fights referees stopped due to injury), they found “no good evidence that they can help prevent concussion, and paradoxically, they may even encourage players to take greater risks.”
The studies that the decision was based on are:
Use of Head Guards in AIBA Boxing TournamentsA Cross-Sectional Observational Study:
Results: Both studies show that the number of stoppages due to head blows was significantly decreased without head guards. The studies also showed that there was a notable increase in cuts.
Conclusions: Removing head guards may reduce the already small risk of acute brain injury in amateur boxing.
Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012:
Protective equipment—mouthguards and helmets
There is no good clinical evidence that currently available protective equipment will prevent concussion, although mouthguards have a definite role in preventing dental and orofacial injury. Biomechanical studies have shown a reduction in impact forces to the brain with the use of head gear and helmets, but these findings have not been translated to show a reduction in concussion incidence. For skiing and snowboarding, there are a number of studies to suggest that helmets provide protection against head and facial injury and hence should be recommended for participants in alpine sports. In specific sports such as cycling, motor and equestrian sports, protective helmets may prevent other forms of head injury (eg, skull fracture) that are related to falling on hard surfaces and may be an important injury prevention issue for those sports.
However studies did show that headguards can protect against other types of injuries to the head, and that when hit the headguard can reduce the chance of concussion:
Boxing headguard performance in punch machine tests:
Methods A linear impactor was developed, and a range of impacts was delivered to an instrumented Hybrid III head and neck system both with and without an AIBA (Association Internationale de Boxe Amateur)-approved headguard. Impacts at selected speeds between 4.1 and 8.3 m/s were undertaken. The impactor mass was approximately 4 kg and an interface comprising a semirigid ‘fist’ with a glove was used.
Conclusions The data support the opinion that current AIBA headguards can play an important role in reducing the risk of concussion and superficial injury in boxing competition and training.
The above test was studied the effects of a sure hit on the head and doesn't take into account the dynamics of a boxing match, missing and avoiding hits.