Harmattan in West African subcontinent occurs between the end of November and the middle of March. It is characterized by dry and dusty northeasterly trade wind. This period usually comes with dryness and dust because there is little amount of water in the atmosphere ( low humidity). In most places, the temperature is cold, but can be hot in some places depending on circumstances.

When the harmattan blows hard, it can push dust and sand all the way to south America. In some West African countries, the heavy amount of dust in the air can severely limit the visibility and block the sun for several days comparable to heavy fogs. The Harmattan brings desert-like weather condition, it dissipates cloud cover, lowers the humidity, prevents rainfall formation and sometimes creates big clouds of dust which can result to sandstorm. The effect caused by this dust and sand stirred by these winds is known as the Harmattan Haze.
This season may come, for many people, with unwanted adverse effects.

For, instance, Harmattan increases the spread of infections or diseases such as cold, cough, catarrh, dry skin, measles, eye defect, triggers sickle cell carrier, asthma etc.

Let's look into some of these things below:
http://www.naijaverify.com/2017/12/how-nigerians-can-stay-safe-during.html?m=1

Harmattan is my best season.

I love harmattan

That's very good. You should, nonetheless, try to stay safe through out the season. Isn't that right?