Problem: Everyday life involves frequently moving between areas with different risks of infection:
(i) safe area, such as a home or a car,
(ii) minimal risk area, such as a hallway or staircase with no people around,
(iii) moderate risk, such as shopping in a supermarket or attending school with some people around, and
(iv) high risk area, such as riding on a subway with many people close by or when social distancing is not observed.

An improved personal protection equipment must allow to adjust the extent of protection depending on the situation. It should also be easy to wear, lightweight and not look like medical equipment.

Face masks are commonly used but not ideal: it is harder to breathe, the face under the mask is sweating, one cannot eat or drink. Face masks are unsightly and do not allow others to see a full face of the person.

Solution: A novel respirator is built into a baseball cap. It has three main components:
1. An airpump pushing ambient air through a sterilization chamber to form an air curtain in front of the face,
2. A face shield that is lowered down or raised up protecting the face, and
3. Three fabric flaps to protect the sides and back of the head.

The sterilization chamber is equipped with several UV light-emitting diodes (LEDs) operating in the UVC range of wavelengths close to 265 nm. The chamber has no filters to minimize airflow resistance. The airpump is selected to provide 7-10 l/min of airflow. A child version may utilize a scaled down airpump.

The pump and LEDs are powered by a rechargeable built-in battery. Alternatively, a plug-in wire is provided to connect to a power source when the user in staying in the same place for a long time (for example, a cashier in a store).

In use, the minimum level of protection is achieved by only activating the air curtain to providing sterile breathing air to the user. The user can easily speak, eat or drink and the face is visible to others.

At an intermediate level, the face shield to lowered down – partially or completely. Sterile air flow continues to flow inside the shield. Partial lowering allows to eat and drink such as in a restaurant.

Maximum protection is achieved by unfolding fabric flaps to protect the head on all sides. Sterile air flow creates positive pressure inside the respirator to avoid risk of infection when in close proximity to other people.

The air handling component and the face shield are detachable for easy cleaning. The cap itself is machine washable.

The no-mask respirator allows adjusting protection up and down depending on the surroundings. It is easy to wear for a long time, does not obstruct the face, and closely resembles a conventional baseball cap – making it more acceptable for everyday use.