Babies have a way of expressing their needs. There are lots of reasons why your baby may cry, the following are few of the reasons:
1. Wet Nappies
When babies are wet, they tend to cry out their desperation to have a change of nappy. Wet nappies can easily irritate their skin thus causing heat and rash if not changed regularly. You don't wanna see your baby cry his/her eye out when you see that.

2. Hunger
When babies are hungry, they can easily cry to express their needs. Babies that are fed exclusively on breast milk can easily get hungry because the milk is quite watery and it is composed majorly of water between 40-50%.

3. Body Heat
When kids are wet, body heat can easily result. body temperature can easily increase especially when under heat weather conditions. If its a newly born baby, they may not react because they are still getting used to the environment and more so, the uterus where they grew up before birth is always a very warm environment, but as time goes on, as they aged, they begin to react to extreme heat and increase in body temperatures, thus triggering their cries.

4. Thirst
When babies especially babies over 24weeks, has started drinking water, they can easily adapt to that condition thus making them thirsty because they urinate a lot during the day which most times is normal, thus the need to constantly refill their tummy but on a more graduated measure to avoid bloating.
Sometimes babies need their back to be rubbed, sometimes they want to be cuddled, wants to be reassured of their mother's love.

A short history on cortisol
Cortisol is a steroid hormone, in the glucocorticoid class of hormones, and is produced in humans by the zona fasciculate of the adrenal cortex within the adrenal gland. It is released in response to stress and low blood-glucose concentration. when their is extreme stress, especially oxidative stress, Cortisol can be produced.
Cortisol is a class of steroid hormones which is normally released when stress is setting in and their is shortage of glucose in the blood which could trigger the conversion of fat droplets into energy producing organic molecules, so this may wear out your baby and in turn could cause brain damage.

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Culled from my blog..