dirt deposits on arms

hi there. i have dirt deposits on my neck, arms, and everywhere else i sweat. As far as i know, i have good hygiene (i take a shower/bath everyday with bar soap) but these dirt deposits never go away. i have tried things like lemon scrubs, skin cleansers but nothing seems to work.
any ideas

[Dr_Aparna]

Hi,
These are not dirt deposits but areas of hyperkeratosis/hyperpigmentation or if associated with itching/burning sensations could be a fungal infection of the skin folds.
Hyperkeratosis is a thickening of the skin, hyperpigmentation accompanies this type of hyperkeratosis.
Most treatments are aimed at softening the keratin and removing the thickened skin. This may be accomplished with topical creams that contain as the active ingredient salicylic acid, alpha-hydroxy acid (lactic or glycolic acid), urea, or tretinoin.
For the discoloration that often accompanies the hyperkeratosis, skin lightening creams may also be used like Hydroqinone 2-4%.
ref:http://www.brownskin.net/hyperkeratosis.html
If it is a fungal infection then application of OTC anti-fungal creams/ointments can be used to treat it.