T-shirts were originally designed for union laborers as an under garment to be worn beneath their uniforms. They were universally considered underwear, rarely ever worn in public. In the late 1800s, it was illegal to wear them as a stand alone garment in public!
The lightweight undergarment was quickly adopted by the military to be worn under uniforms, but could be worn alone at the discretion of the commanding officer. After WWI, soldiers would return home, taking this new fashion with them.
The popularity of a t-shirt as an outer garment further surged thanks to Marlon Brando and his role as Stanley Kowalski in A Street Car Named Desire.Brando’s smoldering performance in both the play and 1951 movie caused a nationwide spike in the sale of T-shirts, proving to the world that the t-shirt could be a sexy, stand alone garment.