It sometimes affects the armpits, chest
the groin area.
Stress, fatigue (pregnancy
/ lactation in
your case), weather extremes, oily skin and infrequent shampooing or skin cleaning & severe medical illnesses make it worse. People with seborrhoeic dermatitis produce too much sebum (the natural skin oil). Later, pityrosporum yeast, grows excessively in the sebum, sometime along with bacteria, making the dermatitis more persistent.