The Crowded Hair Count

At noon on census day, a city has more than one million residents. Imagine that every resident’s scalp hairs could be counted perfectly at that exact moment. Some residents may have none, while no resident has more than 150,000 hairs. Without knowing anything about hairstyles, age, or hair loss, can you be certain that at least two residents have exactly the same number of scalp hairs? Explain whether the information forces this conclusion.