The splitting of two strands of DNA, known as DNA denaturation or DNA strand separation, is primarily caused by breaking the hydrogen bonds that hold the complementary base pairs together. These hydrogen bonds form between specific nitrogenous bases: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). Disrupting these hydrogen bonds leads to the separation of the two DNA strands.

Several factors can cause DNA denaturation:

1. Temperature: Increasing the temperature of a DNA solution can provide enough thermal energy to break the hydrogen bonds between base pairs. As a result, the DNA strands begin to separate, resulting in denaturation. This process is often referred to as "heat denaturation" or "thermal denaturation."

2. pH Changes: Extreme pH conditions can also disrupt the hydrogen bonds in DNA. Highly acidic or alkaline environments can alter the ionization states of the nitrogenous bases, affecting their ability to form stable base pairs. Consequently, the DNA strands may denature.

3. Chemicals and Solvents: Certain chemicals, such as formamide, urea, or sodium dodecyl sulfate (SDS), can interfere with hydrogen bond formation between base pairs. When added to a DNA solution, these chemicals weaken or disrupt the hydrogen bonds, leading to DNA denaturation.

4. High Salt Concentrations: High salt concentrations can also influence DNA stability. The presence of ions in salt solutions can interfere with the electrostatic interactions between the negatively charged DNA backbone and positively charged ions. This interference can destabilize the DNA structure and cause strand separation.

It's important to note that DNA denaturation is not always a harmful or irreversible process. In some cases, such as during DNA replication or gene expression, the temporary unwinding or denaturation of DNA is essential for essential cellular processes. However, under extreme conditions or when DNA is damaged or degraded, denaturation can become irreversible and disrupt cellular functions.