Dirty underwear with bacteria and fungi can potentially contribute to skin irritation or infections in the genital area. This may not directly cause blisters, but it could lead to conditions like dermatitis or a yeast infection which might present as redness, itching, soreness, or bumps on the skin. It's essential to maintain good hygiene by changing into clean underwear regularly and washing your intimate clothing properly to prevent any potential issues. If you have concerns about blisters or other symptoms in that area, consulting a healthcare professional for an accurate diagnosis and appropriate treatment is advisable.