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Ionized nebulae are key to understanding the chemical composition andevolution of the Universe. Among these nebulae, H~{\sc ii} regions andplanetary nebulae are particularly important as they provide insights into thepresent and past chemical composition of the interstellar medium, along withthe nucleosynthetic processes involved in the chemical evolution of the gas.However, the heavy-element abundances derived from collisional excited lines(CELs) and recombination lines (RLs) do not align. This longstandingabundance-discrepancy problem calls into question our absolute abundancedeterminations. Which of the lines (if any) provides the correct heavy-elementabundances? Recently, it has been shown that there are temperatureinhomogeneities concentrated within the highly ionized gas of the H~{\sc ii}regions, causing the reported discrepancy. However, planetary nebulae do notexhibit the same trends as the H~{\sc ii} regions, suggesting a differentorigin for the abundance discrepancy. In this proceedings, we briefly discussthe state-of-the-art of the abundance discrepancy problem in both H~{\sc ii}regions and planetary nebulae.

The abundance discrepancy in ionized nebulae: which are the correct abundances?