Your question is quite an appreciative one as this problem is often found in males but they are most of the times not ready to discuss it with a doctor or a mate due to a feel of male supremacy and ignorance. It should be understood that even males who are considered as less prone to infections and genitals diseases can also have problems like this and they can turn ugly if not treated properly on time. Now, coming to your problem of development of mould on penis, it is nothing but smegma which is a yellowish development on the foreskin. This develops just because of improper cleaning of penis after sex or masturbation. If you have an active sex life then you should always keep your penis cleansed with either a cleanser or by a sanitizer. This is done so that you keep healthy and your partner is also kept healthy and there is no room for sexually transmitteddiseases to occur. If you see any kind of unwanted development on your penis then it is advisable to take to take a view from the doctor or genitals specialist because if these types of things are ignored then they can take a much uglier look. It is quite a common thing if penis is discharging unwanted liquid or some kind of skin swelling when the genitals are not kept in a healthy environment. This is the most important thing as the penis and the scrotal sacs should always be washed properly on daily basis as these are the most sensuous part of the male body and are prone to infections. Failing to do so might lead you to contracting any kind of sexually transmitteddiseases which are not good for and your partner. You should go for a check up as early as possible. Wishingyou good luck.